The NEXUS office at Pearson was extremely convenient. As a card holder, I walked in, signed in with my name and reason for visiting (update data), and took a seat. 15 minutes later I was seen by an agent and walked out the door. One of the best parts about this location is that there is free wifi at Pearson.
Now from what I hear and from personal experience, it's pretty much impossible to book an appointment/interview here for a few months. If you want to visit this office, the best option is to book an appointment as far out as possible and check back regularly to see if a spot has opened up.