Originally Posted by
YYZFlyboy
If you're flying international > USA via YYZ you will have to pick up your baggage, go through the CBSA process (Customs 'A') then go through the US Homeland Security process in YYZ.
Because YYZ has pre-clearance there's no way around it. The bonus is, of course, when you arrive at your US destination there's no US Customs there, it's like a domestic flight arrival. If you've been trhough US customs in places like LAX then you'll know that's a great benefit in itself.
Incorrect - While you take the escalators down to customs A, you then take a hard left and proceed back up to the us connections area. You don't actually go through customs A.