How can a Canadian political candidate make her campaign promises legally binding, and make herself personally liable if she broke her promises?

Frame challenge: this is unrealistic and undesirable.

(but oh so very fashionable these days)

Let's start looking at the cited page:

An Ontario Superior Court judge has absolved Ontario Premier Dalton McGuinty of breaking an elaborately signed contract promising not to raise or create new taxes, saying anyone who believes a campaign promise is naive about the democratic system.

How about the case when a politician inherits worse-than-expected numbers from their predecessor and therefore has to raise taxes?

More generally, in most cases an election puts in place someone who is not unconstrained in what they can do. By checks and balances, which the same voters doing the complaining usually also insist upon.

But also by the opposition, which rarely is incentivized to assist in getting things done. And by lobbying by those affected negatively by a significant policy change.

It is frequent that a politician genuinely tries to carry out their campaign promise and is stymied in doing so. And, guess what, that is also part of the democratic system.

Or, sometimes they mature once in office and realize that their well-intentioned ideas can't be carried out as intended. If I were living in NYC, I'd be relieved Mamdani is slow-walking some of his flakier ideas...

And the one type of policy quite capable of being passed...

Are tax cuts. Which are the subject of the cited page. Which always sound good, don't they? Except when we don't cut spending, which rarely happens and we are running on ever-increasing budget deficits.

Most of the Western world sees interest rates on debt a swelling spending item which in many places comes in as top tier items, right after health and education and the like.

It's easy, in Canada, to see a provincial or federal politician getting elected on a promise to cut taxes. It's also easy to envision how negative that would be in the long term when coupled to existing budget deficits and debt loads.

All the easier from observing the effects of the One Big Beautiful Bill in our southern neighbors.

Cutting taxes, when done irresponsibly, without cutting spending, is the best way for a politician to buy themselves popularity while kicking the can down the road to future generations. In fact, high taxes now are probably a sign people chose the easy way a few decades back.

This is also an indictment of press coverage, readership and electorate expectations.

There is a real tension in democracies between campaigning - a popularity contest and governing - calling for good management. In the past policy promises would be scrutinized by the press during campaigning, but now focus for much of it is on identity politics, because... that's what the readership longs to read. Few could be bothered to figure out if Mamdani's spending promises were fiscally doable. Or if campaign-Trump's tariff ideas made any sense (those promises might have been better shelved).

No, most of the energy is spent on shooting down the opposition, while lauding one's chosen candidate without looking too closely at how their sausage is being made.

So once the rubber hits the road during the governing part, often stupid ideas get quietly shelved and that is not necessarily a bad thing.

As the cited judge says...

Punish that party comes next election. And since Canadians often look at US actions, there is the "read my lips" precedent to take inspiration from: having been elected on a no-new-taxes platform, Bush Sr. resoundingly lost his reelection bid after breaking that pledge.

p.s. I am certainly not pro high taxation. What I am pro is spending within our means.

p.p.s. If a politician wanted to deposit a bond of their own money into escrow and use that as campaigning tool, I don't see why that should not be allowed. But it should not be a requirement. And consider this: such a system would penalize politicians who are not already wealthy.

This is a legal impossibility

If the candidate were to attempt to make a legally binding contract with the world, or some part of it, like her constituents, this contract would be void for being against public policy.

A parliamentarian’s overriding legal duty is to the Monarch, not to her constituents or anybody else. Note that in this context, the Monarch is the personification of Canada, not the individual who currently holds the position.

This is a requirement of the Constitution Act 1967 which states: “Every Member of the … House of Commons of Canada shall before taking his Seat therein take and subscribe before the Governor General or some Person authorized by him … the Oath of Allegiance contained in the Fifth Schedule to this Act”. The oath itself is: “I, (Member’s name), do swear, that I will be faithful and bear true Allegiance to Her Majesty Queen Elizabeth the Second”. As an alternative to swearing the oath, Members may make a solemn affirmation, by simply stating: “I, (Member’s name), do solemnly, sincerely, and truly declare and affirm that I will be faithful and bear true allegiance to Her Majesty Queen Elizabeth the Second”.

A similar oath is required of Senators. And, for that matter, the Monarch.

Any contract that fettered the parliamentarian in the discharge of their duties, for example, by pre-committing them to a given course of action, conflicts with the law and is therefore void.

Note this is a frame challenging suggesting that the idea is very bad and even dangerous.

This would be a very bad idea as well as dangerous as it would make achieving compromises much harder if not impossible. As politicians are elected alongside other politicians that have different beliefs and goals it is expected that they will work together and make compromises on what they want in order to accomplish their goals. If they where held legally responsible for making those compromises it would prevent them from ever trying to work together.

As an example you have two politicians with different promises

Politician 1:
Promise A
Promise B
No new taxes

Politician 2:
Promise X
Promise Y
Promise Z

It could easily work out that in order to get the higher priority promises A/X completed they could compromise on other things such as a tax hike to ensure that the other priorities had the needed funding.

Thanks to user @ccprog for pointing this out, but for example in Germany or in France any such contract would be illegal.

The German Grundgesetz (essentially the constitution) says in §38:

Members of the German Bundestag...shall be representatives of the whole people, not bound by orders or instructions and responsible only to their conscience.

The French constitution says in article 27:

No Member shall be elected with any binding mandate.

Comparable regulations prohibiting an imperative mandate exist in a number of constitutions. The Venice Commision of the European Council lists

Andorra, Article 53; Armenia, Article 66; Croatia, Article 74; France, Article 27; Germany, Article 38.1; Italy, Article 67; Lithuania, Article 59 – which refers to no restriction of representatives by other mandates; Romania, Article 69; Spain, Article 67.2

In all these cases laws prevent a politician from binding themselves that way.

In the same direction as the frame challenges by @ItalianPhilosopher and @JoeW, it should be pointed out that the discussion about imperative mandates is old, and the most cited negative answer was given in 1774 by the newly elected representative for Bristol to the House of Commons, Edmund Burke. It is considered the theoretical basis for the trustee model of representation:

I am sorry I cannot conclude without saying a word on a topic touched upon by my worthy colleague. I wish that topic had been passed by at a time when I have so little leisure to discuss it. But since he has thought proper to throw it out, I owe you a clear explanation of my poor sentiments on that subject.

He tells you that "the topic of instructions has occasioned much altercation and uneasiness in this city;" and he expresses himself (if I understand him rightly) in favour of the coercive authority of such instructions.

Certainly, gentlemen, it ought to be the happiness and glory of a representative to live in the strictest union, the closest correspondence, and the most unreserved communication with his constituents. Their wishes ought to have great weight with him; their opinion, high respect; their business, unremitted attention. It is his duty to sacrifice his repose, his pleasures, his satisfactions, to theirs; and above all, ever, and in all cases, to prefer their interest to his own. But his unbiassed opinion, his mature judgment, his enlightened conscience, he ought not to sacrifice to you, to any man, or to any set of men living. These he does not derive from your pleasure; no, nor from the law and the constitution. They are a trust from Providence, for the abuse of which he is deeply answerable. Your representative owes you, not his industry only, but his judgment; and he betrays, instead of serving you, if he sacrifices it to your opinion.

My worthy colleague says, his will ought to be subservient to yours. If that be all, the thing is innocent. If government were a matter of will upon any side, yours, without question, ought to be superior. But government and legislation are matters of reason and judgment, and not of inclination; and what sort of reason is that, in which the determination precedes the discussion; in which one set of men deliberate, and another decide; and where those who form the conclusion are perhaps three hundred miles distant from those who hear the arguments?

To deliver an opinion, is the right of all men; that of constituents is a weighty and respectable opinion, which a representative ought always to rejoice to hear; and which he ought always most seriously to consider. But authoritative instructions; mandates issued, which the member is bound blindly and implicitly to obey, to vote, and to argue for, though contrary to the clearest conviction of his judgment and conscience,--these are things utterly unknown to the laws of this land, and which arise from a fundamental mistake of the whole order and tenor of our constitution.

Parliament is not a congress of ambassadors from different and hostile interests; which interests each must maintain, as an agent and advocate, against other agents and advocates; but parliament is a deliberative assembly of one nation, with one interest, that of the whole; where, not local purposes, not local prejudices, ought to guide, but the general good, resulting from the general reason of the whole. You choose a member indeed; but when you have chosen him, he is not member of Bristol, but he is a member of parliament. If the local constituent should have an interest, or should form an hasty opinion, evidently opposite to the real good of the rest of the community, the member for that place ought to be as far, as any other, from any endeavour to give it effect. I beg pardon for saying so much on this subject. I have been unwillingly drawn into it; but I shall ever use a respectful frankness of communication with you. Your faithful friend, your devoted servant, I shall be to the end of my life: a flatterer you do not wish for.

_{The Works of the Right Honourable Edmund Burke. Vol. II. London: Henry G. Bohn, 1854–56. Quoted after this.}

The argument he delivers is a spatial one ("those who form the conclusion are perhaps three hundred miles distant from those who hear the arguments"), but it can easily applied also to the temporal distance: "what sort of reason is that, in which the determination precedes the discussion"? A parliamentarian must be able to change his/her opinion, if the deliberations teach him/her to do so.