It's at the far north end of Terminal 1...go into the Priority Check-in area and walk straight through as far as you can go, at which point turn right and there you will see a podium with an agent about 50m away...you will need to present your Nexus card and boarding pass. Not only will you likely not have your carry-on checked for size but you will also bypass the general security line and I've never had more than 1 - 2 people ahead of me in that area.