Valdez, Alaska. 
From the conversation in ST:TNG "Lower Decks", it isn't specifically said that Riker is American, being from the American Arctic, but it seems clear that he is not Canadian. We know that Canada exists under either United Earth or the UFP from other references, and it is very likely that the U.S. has a similar existence. The federal nature the United States does make it possible that the United States, as comprised of fifty states and one federal district exists, no longer exists, but instead the fifty states having a direct governance relationship with United Earth.
Riker does specifically identify the Enterprise-D as not being American in ST:TNG "The Neutral Zone". He does, however, recognize the significance of the number of stars in the union of a U.S. flag on a piece of space flotsam (ST:TNG "The Royale"); thus he is at least familiar with the U.S. from a historical perspective. Therefore, he is either Alaskan and American, or just Alaskan, and he is certainly a Federation citizen ProfessorTrek 06:59, August 8, 2011 (UTC)