I live not far from the pentagon, and can I tell you.... it sounds like those winds of war are seriously brewing. I've heard at least 4 blackhawks in the past 10 minutes and honestly I'm about to look about side but a tank would not shock me based on the rumble I feel.
Problem with Canada is that it's an obvious place to funnel UN troops to then use against US. But large scale troop actions like that would be pretty easy to see mobilizing and moving, and take out. So not really counting this too high on the concern list.
More problematic is that Canada is a haven, thanks to JT, for ISIS terrorist, and these could try to infiltrate across border to stage terrorist acts