NFL teams are highly unlikely in Canada.
Because of the schedule in December and January, teams would either have to play road games during those months (and what do you do if you get a home playoff game?)
There are three domed stadiums in Canada to counteract winter conditions: Toronto's Rogers Centre (Blue Jays stadium) which seats 50,000; Olympic Stadium in Montreal (whose roof may or may not be covered depending on how mothballed that stadium is) seats 56,000 and is where the Expos used to play; and BC Place Stadium in Vancouver which seats 54,500 and is still the home of the CFL's BC Lions.
The largest stadium in Canada is actually Commonwealth Stadium in Edmonton at 56,400 (outdoor NHL game in 2003) but is not covered.
Toronto is the only possible city to get a team in my mind, but its population is more and more made up of people whose familiarity with and love for football is nil.
Based on my eyeball test going to Calgary Stampeders CFL games, new Canadians are not choosing CFL football (nor many sports in general) so convincing them to go to NFL games at possibly an even higher ticket price than CFL games is mildly optimistic.
I am not picking on criticizing their choices, but as Toronto is the most likely city in this conversation and half Toronto's population being new to the country, the point has to be made that they would need to be taught to love football, and Lord knows the CFL has had a hard time doing that, so the NFL might have trouble as well.