The way things work in Canadian airports, (YOW, YYZ and perhaps YVR) is that lane assignments (eg NoS or NoS-less lanes) are determined by lot. All passengers (except Nexus and other trusted traveler programs) go through the same pre-inspection maze. At the front of the maze, you step on a scale-like mat and by apparent randomness, assigns you a direction and/or a specific screening lane that you must follow.


W/r/t the NoS in YYZ, they have them in the domestic checkpoints and I have seen them in operation. I wasn't assigned to a lane that included the NoS, so I would not know personally the options available to me on a first-hand basis. I did get my first opt-out experience at the transborder checkpoint and was told I had two options, NoS or sweeping-action frisk (this was before the "enhanced" gobbledygook was instituted).