It's incredibly hit or miss with US-based carriers and, as suggested, it's easier to bring your passport.

However, being that you're originating from a Canadian airport they're not likely to give you too much grief for just having a NEXUS card when it comes to the doc check at the counter or the gate (although returning to Canada from the US you might get some push back - though I've always been able to fly between the US and Canada with just my NEXUS card). That isn't to say they won't ask you for a passport both ways, but I usually just tell them in a friendly tone that I've always been able to travel on just my card. Maybe I've just been super lucky?