Tracy--has to be a newcomer in the tradition of Ricki Lake, Marissa Winokur (general newcomer, anyway), and Nikki Blonsky
Edna--Eric Stonestreet...the vocals shouldn't be an issue, as Harvey Fierstein is no Maria Callas, but was PERFECT for the role.
Wilbur--Bryan Cranston. He was quirky, strange, and funny on Malcolm in the Middle, and I think he could totally do the role justice. An overall versatile actor.
Link--Darren Criss seems like a pretty safe bet, he could pull it off adequately.
Velma--Chenoweth would be deliciously perfect, but Jane Krakowski would also be a fantastic match.
Motormouth Maybelle--can we bring back Darlene Love? Not only is she a music legend, but she did it on Broadway and had some recent exposure after the 20 Feet From Stardom doc. Patti LaBelle would blow the damn roof off the place, too.
Seaweed--NeYo? Maybe? I was pleasantly surprised by him in The Wiz, but I'm not sure how young he could read. Maybe an unknown would be a good idea for this role as well.
Penny--unknown. The younger kids should all be unknowns, now that I think about it. As per the movie, it seems to make sense to cast bigger names as the adults, and fill the younger roles with some fresh new energy.
Corny Collins--not sure how his acting is, but I can picture Michael Buble doing a fine job. He has a smooth, classic voice, and he's got the charm for it.
Inez--unknown, as previously stated.
Just because it would be cute, let's have cameos from past cast members...any of the 3 "original" Tracys, John Waters (maybe as Mr. Pinky?), etc.