When you are told that two voices from the original Happy Feet will be returning for the sequel, you can likely guess who. Elijah Wood is a no-brainer considering that he voiced the title character, and Robin Williams makes sense considering that he voiced just about everybody else.
Robin Williams, Elijah Wood for Happy Feet 2
Wood and Williams are currently in negotiations with Warner Bros. to reprise their roles in Happy Feet 2. Elijah would return to voice Mumble, while Williams would be confirmed for both Ramon and Lovelace. If all goes to plan, the actors will be whisked off their feet this January to go record their voice tracks over in Australia. Not exactly the place I'd think of for finding motivation for a character located on ice, but whatever works I guess.
The original Happy Feet took in ~$198 million at the domestic box office during its theatrical run, winning some awards in the process.