Hmmm, well Canada now has an interest in all of Airbus's product line up, even if none of it is made there. And whatever the "rules" are a country can do whatever it wants if it decides that the reaction of other countries is not going to be too troublesome. The US does that all the time!
But I doubt anything like this will happen. Boeing's name now has a lot of mud stuck to it, and that's certainly going to be part of an airline's purchasing considerations. That's probably enough for the Canadian government to achieve the desired effect in the long run without resorting to imposing punitive trade tariffs against Boeing.
There's probably some other US airlines that are worried about being forced to buy Boeing. It's hard to be competitive on international routes if you're unable to buy the best aircraft due to domestic political machinations. A trade war is not in their interests either.