Most Zelda Cube characters remain a mystery. There are the ones we can guess will be in it and the few that are confirmed, such as Link. It's obvious that the famous Hylian hero will be the main guy in this game. Who else? Nintendo can change the console, they can change the graphics, but they just can't change this. Ganon/Ganondorf was confirmed originally with the old shots, but he has yet to be seen in the cell-shaded version. The presence of Zelda is still a mystery.
There are also some Zelda-regulars that aren't confirmed but are very likely to appear. Some of these are the fairies of the game, Link's horse Epona, and perhaps some other Hyrulian races like the Kokiri, Gerudo, Goron, and Zora.
Expect some new ones also, and perhaps some that we haven't seen since previous Zelda games. As more characters are confirmed, this page will be updated.