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

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.