outside edmonton and calgary the vast majority of the canadian population is within 100 miles of the US border. now imagine the logistics of a land invasion from northern canada. Shortest distance would be 1600 miles of wilderness. If you went from alert it would be more like 2500 miles of wilderness and several water crossings. All while you are being absolutely pummeled by US air support. It would be a suicide mission that would make the Kokoda Track campaign look like a boy scout trip.
It is such a different situation in europe. Helsinki is 100 miles from the russian border with road, highway, and rail connectivity and within reach of most of Russias air power.