Funny thing here....I'm not sure and this is my neck of the woods.

I believe you clear customs in Toronto with your baggage then you must go to the connection desk on the arrivals level to check your bags for your Transboarder flight to the USA. We treat this flight as an international flight airside.

Remember T1 is the international terminal and T2 is the domestic-transborder terminal in Toronto. This means you will need to transfer between the two Buildings.

Regards YYZAC