Let's not joke hear CA doesn't stand a chance. They've no nukes. They lack economic power. And they don't have a cultural identity beyond "hey we aren't America". The last thing Canada wants is to fight a global super power.
Sure, maybe they’d win the invasion easily, but can they win an occupation of a hostile populace for an indeterminate duration? The 21st Century repeatedly suggests the answer to that is “no, eh”.
occupation of people who are virtually indistinguishable at a glance. Just ask the Russians how that worked out in Eastern Ukraine, the only way they could ever secure the place was by killing pretty much everyone.
The last thing the US wants is to be a pariah to the UK, Australia, NZ and South Africa. Them old commonwealth loyalties run deep. Not to mention France would take extreme exception to Quebec.
Even if we didnt intervene militarily we all love Canada, It would be economic suicide.
"Hey we aren't X" has earned the presidency of the United States every 4 years for at least as long as I've been alive. Never doubt the power of "hey we aren't X".
Germany, Austria and Switzerland speak German, and are still different countries.
US, UK, Canada, NZ and Australia speak English, and are different countries
France and Belgium speak French, are different countries.
The entire Arabic speaking world is spread across like 20 countries.
Russia and Ukraine both speak Russian*, and one tried to merge with the other, violently, and are now bitter enemies probably forever..
Is "Fuck off and leave people alone" an option in peoples brains?
Just think of all those US soldiers slipping and sliding across the zamboni fields while the graceful Canadians glide on their skis. No attacker stands a chance.