YVR nexus office is opposite USA check in counters as mentioned. It is only for the Canadian portion of the interview.
For the USA interview, you have 2 options.
1. Book at any local office (such as Blaine). These appointments usually are available only a few moths out.
2. Choose to do it the next time you fly out of YVR to the USA. After going through USA customs, there is a waiting area all the way to the left of the hall and they will call you to complete the interview. I would try not to go during very busy times as it can be a while.