I'm undecided on if Canada having nukes would be good or bad.

You're right that the more people that have them, the more likely someone will use them, which would be extremely bad.

But if the choices were: 1) USA invades Canada, 50,000-2,000,000 Canadians die (plus some number of Americans). 2) Canada has nukes, USA does not invade, no one dies.

How can you balance the existential danger of another country having nukes against so many deaths?

(All potential deaths, yes. But we're already solidly in theoretical territory. I sure can't accurately estimate the chances of the US invading Canada in all potential scenarios, nor can I estimate how much more likely Nuclear Armageddon is if one more country has nukes)

Two bombs killed anywhere from 150,000 to nearly a quarter million people. Who do you think those people were?

Mostly civilians, because the US loves to exterminate innocent people because it's an evil country. The US does not need nuclear weapons to kill civilians by the hundreds of thousands, though, it does that with conventional weapons every few decades.

However, Putin invading Ukraine was seen as “unthinkable”, regardless of what you think of the conflict there. Trump starting a war with Iran was far from a smart decision, and yet it happened anyway.

There's a world of difference between "bad idea that probably won't work" and "bad idea that can't work" - this idea that some craaaaazy dictator can come to power and use the nukes is a misunderstanding of how power structures work.

No matter how stupid or irrational any individual leader is they're merely the head of a much larger apparatus filled with other people who do know what they're doing. The wars against both Ukraine and Iran had a lot of other people behind them who thought it might work. There's a severe shortage of people behind the throne who think using nukes might work.

But you know what? It doesn't matter! You can't take away the any country's nukes, they'll nuke you if you try. That means you have to let everyone else have them to defend themselves and maintain sovereignty. Nuclear proliferation is inevitable, even if you don't like it.