So, here's my defense plan for Canada. Basic philosophy: it is unsafe to wait for an attack.
1. Get public confirmation from NATO that Article 5 applies even if the aggressor is also a NATO member.
2. Send an ultimatum to Washington demanding a public acknowledgement of Canadian sovereignty by the President and confirmation of non-aggression.
3. In the absence of that acknowledgement, sever diplomatic ties, close the borders, and embargo trade. Blow bridges, tear up roads and rail lines.
4. Evacuate Canadian civilians from the border area; probably 300km or more. Yes, this is where most Canadians live.
5. Declare a security corridor of 300km on the other side of the border, in US territory. Any military activity in that area is a sign of imminent aggression and will prompt a defensive strike.
6. If anything occurs, surge forward and take territory. Keep any war on US soil, not in Canada.
The goal is to get Canadians out of harm's way for a shooting war with short-range missiles (500km-1000km); keep something like an economy running, although severely curtailed by the loss of US trade and any facilities near the border; and bring the maximum pain to the US economy, civilian morale, and government.
We can't afford giving an aggressor the benefit of the doubt; too much of our population is within an hour's drive of the border.
If we wait until the US military moves into position to invade, we will have already lost.
We have thousands of kilometers of borderland between the continental US and Canada, as well as Alaska and Canada. Even if the US makes headway into Canada, we can identify areas of the US to occupy. The psychological effect of having US territory occupied by a foreign country would be really devastating on its citizens.
@evan Oh, absolutely. Americans do not know how it feels to be occupied; haven't had it happen since 1812.
I can't guarantee we wouldn't bite back like a rabid dog, but I can guarantee it would fuck with our identity fiercely to have a foreign sovereignty holding our soil.
@mark The more time and resources that were spent dicking around trying to recover the Alaska Panhandle or northern Maine would be time and resources not spent on Canadian territory.
I think the best move would be to hold a lot of rural area or wilderness, not any cities or even big towns (expensive and hard to hold). Make a big red stain on the map on the nightly news, with minimal effort.