Why the difference?

One would hope that if Russia swarmed across to Canada we would back up Canada, our traditional ally.
Although it's always possible Trump would tell Putin, "You get the north half, we'll take the south."

I know your hatred of Israel runs deep, and you can write volumes on why my perception is misguided, foolish, I'm a dupe, etc, but bottom line, Israel is more of an ally than any other nation in the Middle East. The Islamic nations surrounding them have always been an existential threat.

It ain't easy being Jews.

Caveat: All religion is such bullshit! But if we weren't fighting over whose religious beliefs should dominate the globe, we'd be fighting over color, fighting for our rich masters, money, resources, satellite dominance, the moon, water, fishing rights, etc.