Originally Posted by
jmj9905
Do I understand that you are saying I must cleat immigration and customs? That seems strange.
There is no "sterile" transit area within which passengers can move between flights without officially entering Canada. When you arrive from outside Canada, you walk via controlled walkways (first up, then down, via escalators and moving walkways) to the Immigration area (seen in page 3 of the T3 map from the GTAA website):
http://gtaa.com/local/files/en/Maps_T3.pdf