Originally Posted by
Symmetre
I seem to recall one of the T&Cs when you get your Nexus card states you need to have your passport with you to present it if asked to.
That hasn't happened to me once in over 20 years ... and today the camera kiosk just takes your picture and that's that. But technically, you are supposed to have both.
I really don't know the answer, because I choose not to and just bring both. My experience is that there is a non-zero chance that SOMEONE will not accept the Nexus card (Gate agent, random CBSA person when nexus machines not working, TSA person coming home), so I just bring the passport. I even bring it for daytrips across land borders just in case when I do know it isn't needed. I feel the extra effort of bring the passport is a negligible burden to ensure zero problems when others don't know what a nexus card is.