Valve today confirmed that Call of Duty: Modern Warfare 3 will indeed be using Steamworks and sold on Steam.
Taken in light of the franchise's history of being sold on Steam, this isn't exactly surprising news, but with Battlefield 3 giving the service a pass, it's probably worth noting.
The game's availability on the service means that if you want you can pre-purchase the game and start downloading it now, in preparation of the game's Nov. 8 launch.
Activision also reiterated that the PC version of their game will support dedicated servers on day one.