Don't soil your dungarees as this could just be an error, but Luigi's Mansion 2 has cropped up on Play.com as a Wii-U title.
As seen here, the retailer has the game listed as an unreleased title. Mind you, they've also got the price listed as £99.99 in the "new and used section", so the whole thing could be a cock-up.
Still, at least that £99.99 game comes with free shipping!
Officially, Luigi's Mansion 2 is only slated to release on 3DS. It'll be out at some point this year - I don't know when, but probably not today.