There are three steps from Toronto: After getting off the airplane, there is a long walk. Follow the sign to US transfer, where it has three steps: 1. Scan your ticket 2. Wait your name appear on the TV screens, which show your luggage has been processed. 3. Scan your ticket and enter the line at the gate to US custom, then you have another long line for safety check. I remember that in Washington or Chicago, you may need to 取行李并从新托运, in Toronto, it seems not necessary. Canada is the destination of your flight. The form on CA flight is for Canada. You can get the US custom form while waiting for your luggage processing in step 2.