E3 2011 announced Luigi's Mansion 2 for the 3DS, but now it seems that it's also going to the Wii U. At least, that's how it seems according to Play, a retailer in the United Kingdom that has a listing for a Wii U version.
Nintendo, of course, has neither confirmed or denied this apparent outing. There still is not an official release date for Luigi's Mansion 2, so there's always the possibility that Nintendo will confirm the Wii U version at E3 2012. After all, we pretty much assume that Nintendo is going to be all Wii U, all the time at this year's expo.