Just as absurd as the idea that the Ukraine would never join NATO.
NATO invading Russia is far more absurd than Ukraine joining NATO, which was never an absurd idea, at least after the fall of the USSR.
You’re still running under the interpretation that NATO would never invade a country. It’s not Estonia that Russia is worried about, it’s the US. NATO is a proxy for a U.S. v Russia conflict.
I'm operating under that assumption for good reason. NATO, and the US, have absolutely nothing to gain by invading Russia. Furthermore, neither NATO nor the US have much stomach for any war, let alone a war with Russia. The US let Afghanistan fall into the hands of the Taliban because it didn't have the political will to support a war with double-digit annual casualties. The majority of Americans don't want war with Russia. As for the rest of NATO, they don't even care enough to uphold their military spending promises, not to mention their pre-invasion desire for Russian oil. I'm operating under the assumption that NATO won't invade because the idea that NATO would invade Russia is utterly, completely, and in every way absurd.
Canada would get obliterated in a war. Plus they don’t have nukes
That undermines your argument. Russia has nukes, NATO has nukes, America has nukes, but Canada doesn't have nukes. Thus, Canada should have more reason to fear the US than Russia has to fear NATO.
. The difference here is that NATO is backed by the US. If the leader was Estonia, then who would care.
No, that is the chief similarity. In NATO vs. Russia, the US in the main player. In Canada vs. the US, the US is the main player. If Russia should consider NATO a threat because of the US, then why shouldn't Canada consider the US a threat?
If Putin decided today to create a defensive military alliance with Cuba and station some nukes there, we’d all be in outroar.
Do you support a Russian-Cuban “defensive military alliance” with nukes stationed in Cuba?
If it was a defensive military alliance in the same way that NATO is a defensive military alliance, then that would be fine. America isn't going to invade its neighbors or annex their lands, so it would have nothing to fear from a genuinely defensive military alliance.
You have to be crazy to believe the invasion isn’t defensive. There is no offensive reason for Putin to invade Ukraine
Then I'm crazy, because I see no defensive reasons for Putin to invade Ukraine, but I do see offensive reasons.*
*You may point out that such reasons would almost certainly be irrational. You would be correct. The conqueror's desire for power is quite irrational. However, we know from history that it is a powerful motivator.