"Ladies and gentlemen, your Cedar Falls Sycophants taking on the Fargo Furriers". I can see that totally happening.
Well if they decide to expand or move a team into a northern location, I could see a few venues possibly that are not controlled by the NFL.
But a few northern venues not tied to the NFL that could take on tenants.
Carrier Dome - Syracuse, New York
T Mobile Park - Seattle, Washington, Mariners baseball park, but can be configured for football.
Fargodome - Fargo, North Dakota, A bit small, and a small city, but the city has been wanting to expand the dome for years, NDstate sells out every game, if in a few years one of the teams pledges to come and invest in the dome it could allow them to expand to a decent capacity, for a FBS NDState and an AAF or similar Team.
Olympic Stadium- Montreal, Can
BC Place, Vancouver, Can
Rogers Centre, Toronto, Can. I think this is probably the best chance of getting an American style team.
Of course there is always the chance of a place building a multi use facility in the hopes of drawing a team.
Des Moines would be a great location to pull in a team from one of these new leagues, as well as Omaha, and some of these other Pro football deprived areas.