It's worth consiering NORAD (the North American Aerospace Defense Command agreement). Under that, US and Canadian military aircraft have access to each other’s airspace and air bases. Just yesterday there was a joint US/CAN team that shadowed RF planes (bombers?) still outside Canadian territorial waters (12 miles) but probably testing to see how quickly there'd be a reaction. Are we sure we want this cooperation to end?
Trump's like a schoolyard bully, never considering that the little kid he's now picking on might have something he needs.
That said, both Canada and Mexico should consider putting export duties on the products Trump wants to put tariffs on. If Canadian Hydro power's going to be more expensive for us due to tariffs, Canada should 'up' the base price, ditto oil - and Mexican produce, particularly avocados*. The very last thing they should do is try to 'make up' for the tarrifs with price supports.
*most of the revenue for avocados goes to the cartels; might as well collect some duty for Mexico itself.
We're in for some pain.