According to Joystiq,
"a triple A Square Enix" Wii U port is being worked on by Straight Right, who is currently handling the Mass Effect 3 port and an original IP for Wii U.
Joystiq puts Tomb Raider, Hitman: Absolution, and Deus Ex: Human Evolution as likely candidates. My money is on Tomb Raider. It's the biggest name and the only one that has a chance of launching around the same time as the PS3/360 versions. Hitman: Absolution is set to release 2 days after Wii U, but I'd be surprised if a port was ready so close though a release months down the line for the Wii U version isn't out of the question. I mean, same goes with Tomb Raider, but a least it's like 5-6 months from release which gives Straight Right a bit more time. It would be beneficial to launch as close as possible.
I suppose there's a possibility it's the Final Fantasy XIII trilogy with Lightning Returns pending release, but that's a lot work. Then again, they could just port Lightning Returns to somewhat match the ridiculousness of just porting the last part of a 3 part story like Mass Effect 3...