As we look at the art we can see that the series is going into the new direction of the revolutionary war. And it seems as if the Templars are the british this go round. Other things to note is the fact that we have a new character that jumps the time period from the early 1500's to the years of 1775–1783 which is when the war happened. Could the famous first president of the United States be the Assassin on the cover? He is carrying a hatchet after all, don't be surprised if he cuts any cherry trees down!
UPDATE: Gameinformer art shows GW is in AC3!