This seems like standard practice for US airlines, including the part where checking in and going through seat assignment means you have a seat (because it indi

This seems like standard practice for US airlines, including the part where checking in and going through seat assignment means you have a seat (because it indicates you're unlikely to be a no-show). What's different here? Are they communicating to passengers differently? Are they overselling much more aggressively than US carriers / worse at predicting? Do fewer Air Canada passengers accept offers to take a later flight, or do they fly routes where that doesn't work?