If there's an air canada flight and it has seats available by the time you're rebooked (ie, there might be 10 open seats but 20 people that need to be rebooked), you'll probably get on that one instead of making you spend the night at the connecting city. As others have mentioned, whether you get to be rebooked on the air canada flight depends on your status, fare, destination and of course the agent you're working with.