Air Canada is not going to end it's relationship with UA. It makes too much money off it.
Since the universe is venting big time on this incident, we are sometimes reminded that we have a choice of airlines when we fly. We don't have to like all of the choices available either based on prices, schedules or the inability of an airline's staff to solve an issue without it hitting the media. Once it does, it will never go away.
You fly Air Canada because they get you where you need to go, when you need to get there, for the price you may or may not be willing to pay.