Originally Posted by
Oceanrider
if the system in Toronto is anything like Montreal's you first check in with AA and then go through US Immigration (pre-clearance) with all your bags and then hand off the checked bags to the luggage conveyor belt handlers. Even if your bag were ticketed by AA personnel outside, you could just not hand off your bag and proceed with it through security. It is highly unlikely that anyone would question your bag size at that point or at the gate.
I fly in YYZ once a year and the process for checking bags is exactly that you go to the AA desk check in, complete your immigration form, stand in line go through US Customs, clear that and had your bags off then go through security. It is pretty simple and efficient. Always have had great service with AA traveling in and out of YYZ.