I'm convinced that stage leak had real and fake things in it. Even though the guy was wrong with names, he was pretty freakin accurate.
NCD = Not Confirmed or Deconfirmed)
Bowser's Castle - Super Mario stage (NCD)
Jungle Hijinx - DK stage (Confirmed)
Bramble Blast - DK stage (NCD)
Forest Haven - Zelda: Wind Waker stage (NCD)
Yoshi's Story - Yoshi Story stage (Confirmed. It's a Yoshi's Wooly World Stage)
Tourian - Metriod stage (NCD)
Nimbassa City - Pokemon stage (NCD)
Mute City - F-Zero stage (NCD)
Cookie Country - Kirby stage (NCD)
Mt. Dedede - Kirby stage (Confirmed, but I think he mistaken Cave Offensive for this)
Patch Land - Kirby: Epic Yarn stage (May of thought the Woolly World Stage was Patch Land)
Underworld - Kid Icarus Stage (NCD)
Game and Wario - Game and Wario stage (Confirmed)
Rhythm Heaven (NCD)
Magicant - Mother/Earthbound (same 3DS stage) (NCD for Wii U)
Endless Ocean
Nintendo Land (NCD but there was Nintendo Land Music in the Wii U version)
NES Remix (NCD)
Green House - Mr. Game & Watch stage (NCD)
Gyromite - R.O.B (NCD)
Shooting Gallery - ??? (NCD)
Rainbow Cruise (NCD)
Delfino Plaza (Confirmed)
Luigi's Mansion (Confirmed)
Rumble Falls (NCD)
Temple (Confirmed)
Bridge of Eldin (Confirmed)
Pirate Ship (NCD)
Yoshi's Island (Melee) (Confirmed)
Norfair (Confirmed)
Pokemon Stadium 2
Lylat Cruise (Confirmed)
Port Town Aero Dive (Confirmed)
Smashville (Confirmed)
Skyworld (NCD)
WarioWare (NCD)
Distant Planet (NCD)
Onett (Confirmed)
Flat Zone 2 (NCD)
I believe the stage part of the leak is real for the most part.