Usually they have in YYZ special line for Connecting flights I have use it when I fly to YYZ from International to National. If this is your case, use the this line so custom will be faster, I dont know how works for USA airlines but with Canadians Airlines when Im connecting from International to National flight, after custom when I pick up my suitcase fallow conections arrow and drop it in the belt, and then go to the 2nd. floor for the security check point and no needs to check in again.