Originally Posted by
SneakyBoy
Since I generally fly out of YUL on direct flights to the US and use nexus I know what to expect. On sunday however I will be flying YUL-YYZ-PHX and return on Tuesday PHX-YYZ-YUL since AC does not fly YUL-PHX direct. Therefore I will be using Nexus for the first time at YYZ. Anybody care to share some information on the procedure and locations of the Nexus terminals at YYZ? Any information would be of great help

Really simple.
When you go down the last escalator, you'll enter Immigration Hall ("Welcome to Canada" just above the entrance). Walk in, then immediately turn right. Four red kiosks on the right side just before Special Services booth.
That's the most common one I've run into. There is another entrance, you come in on the left side, and they have kiosks there too. In the long run, it's a little faster to use the kiosks on the right side, as the exit from that hall is closer to the machines on the right.