Originally Posted by
wazzuFreddo
Don't you pre-clear customs at YYZ before getting on the plane? Since you go through US customs before getting on the plane it should just be a short walk from Terminal 3 to the international Terminal. I doubt you will even have to go through security.
That was the case the last time I flew from Toronto to SFO.
The OP is concerned about the return flight, not the outbound from YYZ.
Since the SFO-YYZ leg is on AC, things might be a bit more complicated (you might need to talk to AC people at the gate), but you should be able to get home even if you miss your scheduled flight.