I've been to a Canadian Orientation Abroad seminar in March, organized by IRCC and IOM, and they mentioned this common myth.
The truth is, it's not the air carrier's responsibility to make sure you can clear the immigration formalities and board your next flight.
The IOM officer said there have been a few exceptional cases where the air carrier had unoccupied seats on the next flight to the newcomer's destination, and they offered them out of goodwill. We can't expect, much less demand that.
Make sure you have enough time to clear immigration, and, as M.Mostafa and ttrajan already said, immigration will be at your first PoE simply because you'll be boarding a domestic flight afterwards and won't be crossing Canadian border again.