Ubisoft confirmed to CVG that all the DLC released on the other console versions of the game will also appear on the Wii U. This likely does not include the PS3 exclusive Benedict Arnold missions.
As you may know, the publisher plans to release five pieces of DLC and three will form "an all-new single-player campaign" which will be made "available as a continual episodic story that will let players experience an alternate history of the American Revolution".
Other future content will include more single-player missions and new maps and characters for the multiplayer element. So far, PlayStation 3 and Xbox 360 owners can buy a season pass for the content that, as usual, gives you a discount. It also allows early access to the DLC a week before everyone else. It is unknown if the Wii U will receive that when it releases with the console on November 18th in North America.
The Wii U version has been has been said to be "exactly the same" by Assassin's Creed III creative director Alex Hutchinson. So if you were contemplating whether to play it on your new Wii U or your other consoles, you can feel safe in choosing whatever console you prefer.