Just went though YYZ Canadian Customs a week and a half ago. It really depends entirely on the time of day you are traveling through the facility. My flight arrived at 11 PM at night, and customs took all of six minutes. Then again, if I was going through the process at, say, 11 AM there are reports of it taking upward of a half-hour to 45 minutes.
To put it in another way, for those doing a connection from an arriving international flight to another departing flight out of YYZ, the minimum allowable layover is 120 minutes. Airlines won't book you to a connecting flight any sooner. And its for good reason! Four years ago, I had to literally RUN from my arriving gate, go through customs and security, and then RUN to my departing gate just in time to barely make my connection (they were calling my name over the PA and closing the door!). And that was with a layover of just over two hours. YMMV.
Safe and happy travels!