I arrived on Thursday with Nexus with no problem at YYZ as I have for a few years and getting back into the U.S. Now there is the additonal benefit that you don't need to fill out the custom forms. It is part of the checkin on the Nexus machine that reads your eyeballs. The machine prints out ticket you waive at the exit points instead of the manal declaration card.
Don't know if anybody mentioned this but if you want a tour of the city, head on over to Yonge and Dundas (kind of like our times square) and hop on one of those city tour buses. I'm sure they'll make for some interesting sight seeing.
P.S, Yonge Street is longest street in the world so there's your first little fun fact about our city.
Depending on your vibe, try Yorkvile, Queen street, King street is nice. Grab a light bite, people watch and start some random conversations. People are very helpful and friendly here in the GTA, especially with a couple drinks in them. Guys are friendlier and they can probably direct you to better go to places. But you gotta go out