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.