As one who goes through YYZ frequently (it is home base) and primarily to the US they choose people at random - it is not always the first person in line.

Thursday of last week I got selected from the middle of the pack on a flight from SFO-SYD for screening, but I didn't complain or say I am being raped. They are doing their job, I may disagree with it, but they are doing what they are hired to do. If they do it professionally, no complaints - if not, then I complain.