Stages have been confirmed for both versions.
http://www.nintendoworldreport.com/news/37094/super-smash-bros-stages-revealed
A lengthy list of stages has been confirmed for both the 3DS and Wii U versions. Some stages will be classic stages, and each version will have their own different classic stages.
3DS stages:
Reset Bomb Forest
3D Land
Spirit Train
Gerudo Valley
Arena Ferox
Toritmer Island
Living Room
Prism Tower
Rainbow Road
Find Mii
Balloon Fight
Jungle Japes
Wii U stages:
Mario Galaxy
Pyrosphere
Town and City
Boxing Ring
Pilot Wings
Skyloft
Windy Hill
Garden of Hope
Wii Fit Studio
Palutena's Temple
Halberd
