I have been quite embarrassed before at a very busy YVR Domestic security when we attempted that. I showed my card and the first CATSA agent sent us both down the Nexus lane, but once we got to the 2nd, my non-Nexus-holding wife could not produce one, we both had to exit and go to the back of the long line. It was somewhat humiliating! I guess it depends on who's in charge, but don't expect guaranteed access.