It's not all hot air, though I don't think we're in a place where a military intervention would happen. But if Trump can influence/cause some sort of an administrative coup that turns Canada officially or unofficially into an American vassal, he would 100% do it. To borrow from Tim Snyder: History doesn't repeat itself, but it often rhymes.
I would look at the annexation of the sudetenland as an inspiration here. Pre war Germany used a proxy party in the region to promote for annexation, Germany claimed they were rightfully liberating the people of the sudetenland and basically dared the rest of Europe to stop them. Nobody stopped them.
What would happen if a similar regional political proxy (Alberta wildrose?) offered up their region for annexation in a private deal? What if Trump threatened economy crippling trade restrictions (tariffs in the 100's of percentage points, etc) if we didn't allow him to "liberate" alberta?
So yeah, I'm not too worried about tanks across the gordie, but our quislings selling us the fuck out? Its not a 0% chance, let's leave it at that.