I'm sure a few of my fellow Canadians will also chime in ...

If you are flying domestically (inter-Canada) or internationally from YYZ (at least from terminal 1, which my experience is limited to), security is very, very straightforward (and you can keep your shoes on).

US departures follows TSA rules - "randomizer", according to CATSA, is set to 50/50 send people to NoS. The screener doesn't select, you step on the "lucky mat" and get pointed either left or right. left is bad, right is good.
Having had the left arrow three times this fall, the pat down is enhanced. One experience was a grope, two were professional.

A marked difference in TSA vs CATSA seems to be attitude. CATSA (in my experience) have been friendly, polite, informed and they will tell you you can go through the NoS or that you can opt-out.