The danger isn't that the U.S. will take over Canada, the danger is what happens when the U.S. finally gets a bellyful of spilling blood to protect the interests of those who villify it, and pulls back its own military to protecting strictly its own interests. I mean
very strictly - contrary to the hysterical insistence that "it's all about oil," the stakes of the U.S. with regard to domestic petroleum supplies are not particularly high in the Middle East. So we let them throw nukes at one another, so what? China wants the Spratlys? No skin off our nose.
I think that some sort of retrenchment is inevitable whether or not we get tired of the defense freeloaders, and the EU needs to be aware of this much more than Canada. The time for the buildup of regional security infrastructure is now before U.S. economic considerations make it mandatory. The U.S. cannot and will not maintain its worldwide defense expenditure in the defense of a nonexistent empire forever, and self-righteous anti-American rhetoric will not keep the barbarians from the gate.
I think the problem is that we (the US) do not want China (or Russia) creeping into Canada. For all their freeloading faults and fem French accents, the Canuks are a relatively harmless lot. So we have to, for our own sake, save their sorry asses in any such event.
It's like the hard-working brother who has to keep floating his dead beat brother money, just because the family doesn't want to have a homeless relative.
I know that keeps pissing my brother off. 8-)