Trump was very upset with his generals not listening to his insane requests last time 'round. How do I know this? He asked for generals "more like Hitler's generals" in that they wouldn't question him. There's a good chance the military simply won't be on board with starting North American wars.
They wouldn't need to. Soft power would be sufficient to get them nearly everything they want, without risking boots on the ground.
The main risk to us, from a military perspective, is if the USA collapses federally and the states end up fighting amongst each other. The Midwest states will collapse into chaos and feudal fiefdoms, lacking access to trade opportunities (IMO) so border raids there will be the big risk. Actual military occupation might be a concern if the dice rolls the wrong way in the East - Toronto and Quebec are very vulnerable, and sitting on huge reserves of fresh water plus the St. Laurence seaway.
It would be a hell of a thing if Canada ended up with alliances with the southern slaveholding states.
Honestly.... I kinda can. This is an extreme and unlikely scenario, but there's a few things that make me think it's not impossible.
A) Trump has publicly promised to back out of NATO.
B) Trump is generally very pro-Russia.
C) Trump has generally had poor relations with Canada.
If the US backed out of NATO, they'd have a lot of military power sitting idle, and NATO would be significantly weaker, as well as doubly occupied in Ukraine. Russia would certainly be interested in such a thing happening, given the strategic importance of Antarctica, and how much it would take eyes away from them. I also don't doubt for a second that Trump would love to exploit our natural resources, especially oil, and the military importance of the top of the world. Not to mention it'd be an excuse to continue creating expensive military contracts and posturing as tough.
This is of course, mostly fantasy, but Trump is nothing if not unpredictable.
With the US out of NATO, USA aggression towards a NATO ally would provoke a response. Also, NATO is not involved with Ukraine. This means that all of NATO can focus on USA aggression. Considering the significant force difference between a non-NATO USA and the rest of NATO, I imagine that nuclear response as an opener is heavily weighed. Glass Washington D.C., then ask if the USA would like to retreat to US lines before they glass NYC. Primary response would be through UK nuclear submarine along the Atlantic.
Imagine if the author came out and simply said "What the Likud party is doing is wrong on every level and must be stopped".
Imagine doing that instead of saying Hamas is justified in their actions by painting a narrative around the US occupying Canadian land and asking us to imagine "what Canadians would do".
Speaks volumes about the people pushing such a narrative.