Except that it is!!!!! CX and AA use T3 in YYZ, which is a privately owned for-profit terminal, and does not provide the international transit service that YVR provides!

Sadly the OP must clear immigration and customs at YYZ, though AA at MIA should tag the bag through to BKK. After clearing customs there is a bag drop area just outside the customs exit door. Alternatively if not tagged for the CX flight the bags must be taken upstairs to CX check-in. Good luck making the connection, it is a bit tight (really depends upon your immigration and customs status, which can be a bit strict at YYZ).