When Mass Effect 3 is released for Wii U, the disc will come pre-loaded with the recently released extended cut DLC that expands the game's ending with new cutscenes and dialogue. BioWare's Michael Gamble confirmed as much in a chat with Siliconera, though he made no mention of WHEN we might see said Wii U port. Presumably sometime after the console is released this fall.
Gamble also made no mention of the other DLC released so far for Mass Effect 3, all of which is tied to the game's Galaxy at War multiplayer mode. One would assume that it's all packed in as well, but with the continued deafening silence from post-E3 Nintendo in the realm of all things Wii U it's really still too early to be making any assumptions.