The question of why US forces are being called upon to shoot objects in Canadian airspace is hardly off topic on a post about US forces shooting down objects in Canadian airspace.
Due to NORAD, Canada and the continental U.S. are a shared air defense zone.
In this case, USAF had been tracking/following the balloon since before it crossed from Alaska into the Yukon, so they although F-18s from Cold Lake had been dispatched, the U.S. F-22s already on-scene took the shot.
Canada has openly encouraged US air power in it's air space since the cold war. They really like the idea of sharing defense with the US. We have a bunch of early warning radars in their territory, and share lots of info about them.
