You are supposed to have an iris scan to be able to use Nexus to fly. You can get it an any Canadian Nexus office (we got ours at YYZ, where we stopped when driving to Toronto from Detroit - no appointment necessary). When you enter Canada by air the Nexus kiosk scans your card, asks you questions, and then you have to look into a little mirror attached to the kiosk for it to verify your iris scan matches.