Of course it all depends on where you cross into the USA ... they have to have the Nexus machines ... the urls above should tell you where all the systems are in place.
According to the Canadian url:
NEXUS is offered at the following airports:
* Vancouver International Airport
* Toronto Pearson International Airport
* Ottawa Macdonald-Cartier International Airport
* Montréal-Pierre Elliott Trudeau International Airport
* Halifax Robert L. Stanfield International Airport
* Calgary International Airport
* Winnipeg James Armstrong Richardson International Airport
* Edmonton International Airport