On the positive side though, a possible invasion of Canada through British Columbia would be extremely difficult to undertake in this case. Here is the picture right here:
Look at the ones that I've circled in here. Red circle indicates the Coast Mountain ranges, and orange circle indicates the Rocky Mountains. Any potential amphibious landing would be difficult in itself, but BC is also protected by two islands, Haida Gwaii and Vancouver Island. If any plausible invasion of BC is to be successful, those islands would have to be captured. Haida Gwaii though, doesn't have anything of value for an invading army, but Vancouver Island has something of value: it is more populated, and Victoria is also the site of the Esquimalt naval base. Controlling Vancouver Island would be crucial, because it would then allow an invading force's naval assets to blockade the city of Vancouver through the Straits of Georgia. Yet, the Coast Mountain range is a large gap between Vancouver and Prince Rupert, meaning that the only way to advance through the heart of BC would be to capture those two cities mentioned.
The most idealistic thing for the Canadian military to do in this case would be to turn the Coast Mountains into a redoubt, or a combination of the Maginot Line and the Alpine Redoubt, and to do the same thing with the Rocky Mountains. Pinning an invasion landing force in the Coast Mountain range could buy enough time for Canadian military reinforcements to arrive in BC, and to repel the invasion force. At the same time though, forming guerrilla forces and stationing them in the forests throughout the BC interior would also help slow down any enemy advance, should they break through the Coast Mountain Redoubt, as they would be too tired by the time they reached the Rocky Mountain Reboubt. The Prairies is essentially flat ground, making it suitable for large scale mechanized warfare. Therefore, BC would be a suitable place to slow down and weaken any possible invasion force seeking to occupy most or all of Canada. That is, if the invasion came from the west.
