Canada

I don't like unrealistic optimism, but I think there are several reasons to be optimistic. TL;DR: enough US citizens would revolt to make it a winnable war against them, and Trump would back down first.

Not only would the idea of fighting the most powerful military on earth cause hesitation, but they’d be doing it from across the ocean where the us would no doubt have their navy stationed with nuclear submarines, destroyers, and air craft carriers.

That's if everyone in the US military complies with the order, and I think a lot of people would refuse. I also think a lot of citizens would start fighting their own military. It only takes 3.5% of people fighting from within an institution to destabilize the whole thing.

I've continually been surprised at what MAGAs are willing to believe (and then stop believing) and I'm sure that a lot them would buy into the new narrative, but it would be such a blatant and self-destructive abuse of power that a non-insignificant number of them would have to wake up. There are also so many individual actors in right-wing media that a few of them are bound to speak out before they get shut down. Just imagine if someone like Tucker Carlson did a 5 minute address saying "I've supported everything Trump does but this crosses the line."

if Russia is going to become more aggressive, which Trump is obviously empowering him to do, Europe needs to worry about itself.

Other countries have a self-interest in keeping foreign dictators in check; while it's true that fighting the US would make other NATO members more vulnerable to an attack from Russia, the alternative of letting Trump literally go insane with power would be more likely to end in a nuclear apocalypse.

We are right next to them as well meaning they would be able to take us with almost no trouble. So nato would now have to conquer the us not just defend against it.

If the US decides to Blitzkrieg us, yes--at first. As someone who lives within a 1h drive of the US border, I'd be fucked, but the US wouldn't be able to keep that territory; see all the above points. I also think Trump would start a military war in the same way that he started an economic war: announce that he's going to do it, get an unexpectedly strong announced retaliation from Canada and blowback from within his party, delay the implementation, and finally reduce the scope. During that time Canada and NATO would be able to prepare.