Originally Posted by Adam Smith

Your first stop should be checking the app or website to see if it offers you re-booking options. Often it has some pretty good choices, possibly including the flights you're hoping for.

If it's not yet offering re-booking options, give it a few days, it sometimes takes a while for the system to catch up. It might not offer you re-booking options until it has recognized the PHL-YUL cancellation and put you on an alternate routing.