Even if it had been occupied by the US for 300 years, I (a US citizen) would be angry with my government if it didn't use military force to stop Canada (or Mexico) from forming a military alliance with Russia (or China) (provided diplomatic avenues had been exhausted). Letting such an alliance persist and flourish would permanently drastically degrade the security of the US.

Thats exactly Russia's reasoning right now. What is essentially happening is that the US is the aggressor and Russia is simply defending itself from NATO expansion. I am not sure why everyone is just bashing Russia without thinking for 2 seconds about this topic.

That's bullshit. The aggressor is the one who is invading and bombing another country.

The only reason why Ukraine even wants to get into NATO is because Russia has never stopped viewing it as a core part of its Greater Russia imperial restoration project. This is also why the entire Eastern Europe rushed to NATO as soon as they could - because they didn't want to end up like Ukraine did.

The reason eastern europe rushed to NATO is simply because the west was quite wealthy as a capitalist bloc, and the former communist countries viewed the west as a holy grail. If the eastern europeans wanted access to the european markets, they would have to go through EU integration, and of course NATO. Its not like they could join the EU if they still were in a warsaw-pact like military alliance. The truth is, the west had more influence because of their economies.

TBF US attempted to invade/annex Canada twice when Canada was British Canada, AKA nascent US's existential geopolitical enemy. It wasn't until British got displaced from NA (thanks to French) that Canada learned it's better to play nice with juggernaut that is US and eventually integrate with US system, because there is no other path to serenity.

And the argument still works. Even in that hypothetical scenario the USA would still reasonably not allow Canada to join that military alliance. In addition, saying Russia occupied Ukraine for 300 years is like saying France occupied Occitanie, or Germany occupied Prussia, or even Spain occupied Catalonia. There's so many of these occasions in recent history that its basically not an argument. On that note, thinking the same way did also the US maybe occupy Utah?