If you call up you may get a better deal. Personally I would wait and do it as near to the flight as you can. Even try at the Check In Desk. If you have Status you may get an Op-Upgrade as flights to YYZ are very popular for people to go WT+ given the length of the flight.

Personally if it was me, I would speak to the check-in agent and see if I can upgrade there and then. I imagine it would be cheaper