Very wierd indeed, as last winter I had a YSJ-YUL direct flight and wanted to get home earlier, only option was YSJ-YYZ-YUL and paid my 75.00$ change same day change fee right at the airport and got home an hour earlier. Did not feel like waiting at the airport for 5 hours and flight was just about to board 45 mins at the airport.
I thought the only requirement for same day change was to have positive invetory space on the flight (as long as it was not oversold or fully booked, they could accomodate)
Cheers Klover