For quite a while there have been rumors that Lando would pop up in Rebels. Some of this came from comments that Billy Dee Williams has made at various convention appearances about doing something for Lucasfilm, and with him not in the Episode VII cast (yet) most people believe that means he’s voicing Lando in Rebels. As the show is set only five years before A New Hope, it would make sense for him to show up and help the crew of the Ghost.
Scoopster superstar Jason over at MakingStarWars.net spotted a Facebook post by Star Wars Insider that seems to confirm that Lando will pop up in the series:
Recently it was also revealed (via toys) that Obi-Wan would pop up in Rebels, so Lando won’t be the only familiar face in the series.