When entering Canada via YYZ you meet a Customs Officer, not Immigration. If they are unsure about something, your passport or paperwork is not in order etc., they send you to Immigration. Immigration never mans the front lines here (don't know why, they just don't).
When exiting Canada via YYZ you do not interact with Canadian Customs or Immigration, unless there is a problem with your paperwork and cannot leave without them intervening. You queue up, chat with a US Immigration Officer, get passport scanned etc., then go to another line where you go through US Customs.
I don't know what people are talking about with respect to rude service. At one point I transited through YYZ almost weekly to the US and never had any problems with them. They have always been professional and polite (both when I had my US visa and when I did not).
I was through there not too long ago, busy Christmas travel day, and the Immigration Officer and I were laughing and joking the whole time. Maybe I just look like a nice person
(if they only knew
)