Originally Posted by hilton-gold
If the segment is an inbound or outbound international one (regardless of pre-clearance), I all but guarantee you will need to get off. AA requires a security check at each first and last point of entry/exit from/to the USA.
In the OP's instance, this is not correct, as the point of entry into the US is YYZ. I've never flown from YYZ to the US (my experiences there have been only on domestic flights), but if it's anything like YVR, security occurs only after a passenger goes through BCIS/Customs, and connecting passengers do not need to go through security again when landing at the first US airport.
Mike