I would just bring your passport. Also, are you flying from one of the airport designated as accepting NEXUS as the travel document?
"A NEXUS card is a
WHTI compliant document,
[7] meaning that it is an accepted identification document in lieu of a passport for travel to or through the United States from a designated Canadian airport.
[8] A designated Canadian airport is one of the following eight airports:
[9]- Calgary International Airport
- Edmonton International Airport
- Halifax Robert L. Stanfield International Airport
- Montréal-Pierre Elliott Trudeau International Airport
- Ottawa Macdonald-Cartier International Airport
- Toronto Pearson International Airport
- Vancouver International Airport
- Winnipeg James Armstrong Richardson International Airport