If the U.S. were hostile toward Canada or barely capable of maintaining a national defense posture, your military expenditures would have to increase, and that increase would make itself felt.
The sad but very honest truth is that if the US was hostile towards Canada, then we would be incapable of defending ourselves, even if we diverted 100% of the national treasury to defence expenditures.
If you believe the USSR would not have been testing Canada over the last half of the 20th Century in such a climate, you're fooling yourself.
I agree with this point as well, but I disagree that the US stance was to protect Canada. The US stance was to protect itself. That Canada was protected in the process was a beneficial byproduct for us, no doubt. But it was always better for the Soviets to be engaged over Canada instead of the US. We were your buffer state. And while the Soviets would have tested us, they would not have conquered us - the logistics would have proven too difficult. They don't share any land borders with us, unlike the US.
Understand that I am not lauding the impact of our global hegemony, quite the opposite. We should withdraw from NATO, from the Pacific, and from the UN, and do so with no small haste.
I understand your stance on this, and have for a long time. I don't think it will ever happen because there is too much money to be made in the rest of the world, and US-based trans-national corporations believe they have a manifest destiny to take that money. As long as that is the case, you will find yourself embroiled in issues that don't mean a damn thing to the average American, at a high cost in both dollars and lives.