CX operates out of T3 in YYZ and AC from T1. There is no airside transfer from T3 to T1.

You have to clear Canadian Immigration, collect your bag, clear Canadian Custom inspection, catch the shuttle train from T3 to T1 to check-in with AC there. You may expedite the process by web check in for your AC flight in HKG. You will then pre-clear US immigration and custom formalities in YYZ. The process is a lot simpler if you fly AC from HKG. You may bypass Canadian immigration and custom, or at least a simplified process.