The internet rumor mill has been hard at work on these two, attempting to cast them within the Batman universe--and apparently failing spectacularly. Gordon-Levitt is set to play John Blake, a special duty beat cop, while Cotillard has been cast as Wayne enterprises board member Miranda Tate. Neither character is particularly iconic in the Batman mythos, which is probably why the Nolan fan base didn't see them coming.
Personally, I'm just excited to see JGL grace the big screen again. He could sign on to play pretty much any sort of character and I would watch him do it. There wasn't much depth or complexity to his role in Inception, but damn if he didn't look dapper. Dude's got chops, too; I first saw him own the lead in the fantastic indie-noir Brick, which required a good deal of subtlety on his part. I don't know anything about the character of John Blake, but based on this casting decision I think it's safe to say he'll be a stoic, wry badass.
Marion Cotillard has got quite a filmography behind her, too. I have to say I thought she was wasted in Inception. Nolan has never really crafted a complex female character, and Cotillard can do better than portraying the archetypal crazy dead wife that seems to haunt Leo DiCaprio across his films. She received a boatload of accolades for her performance in the gorgeous La Vie en Rose, and I enjoyed her in Tim Burton's Big Fish as well. Here's hoping she has more to work with in the role of Miranda Tate.
The Dark Night Rises is currently slated for a 2012 release. Christian Bale will reprise his role as Batman, while Anne Hathaway will join the ensemble as Catwoman.