[docdeek]

'The West Wing’ had an episode where the US plan to invade Canada was a plot point (https://westwing.fandom.com/wiki/A_Good_Day). Of course there is a US plan to invade Canada - no matter who the president is, the armed forces would try and be prepared for any eventuality no matter how unlikely (in the episode the plan was over a hundred years old, but it existed). Similarly, it would not be unusual for Canada to have war gamed a US invasion.

[IAmBroom]

IIRC, the original, historical plans were developed to counter a scenario where Canada had been blitzkreige-invaded by "another Northern power", as a prelude to launching an attack requiring the US to defend 2,000-miles of border.

It never was about mistrusting Canada. Mexico, maybe, if they were mad; but not Canada.