After some leaked information, Ubisoft has gone ahead and confirmed Assassin's Creed 3 is set during the American Revolution. More will be revealed on March 5th, but Ubisoft released the box art for AC3 depicting the protagonist about to strike a British Regular, potentially even an officer, with a Native American tomahawk. In the background is the American flag as it appeared during the Revolution and members of the Continental Army. All of this speaks to the American Revolution as the backdrop, and the protagonist could even have some Native American blood (some speculation already confirms that). He has the aforementioned tomahawk in his hand, and on his back is a bow and a quiver of arrows. A flintlock pistol is stashed in his belt, so you should have at least one firearm at your disposal.
More will be revealed by Ubisoft on Monday, hopefully including whether or not the PC version will arrive on October 30th with the console versions.