Depending on how many states it splits into, it might make a "North American Football Federation" viable. IOTL, since North America itself has like four independent countries and those four didn't want to partner with the Caribbean, they ended up joining with the South Americans instead to form the Confederation of American Football Associations.
On the other hand, if the USA or Mexico were forced to play just with small Caribbean and Central American countries all the time, their players might not get as good as they did IOTL playing against the likes of Brazil, Argentina, and Colombia all the time. The legendary 2006 USA-Mexico World Cup Semifinals might be butterflied away.