This thread used to live in the Rumors section, but as it's been confirmed that Meryl Streep is part of the cast, I went ahead and moved it here.

As of the time that I moved it, she is assumed to be voicing Aslan, but that has not been officially confirmed.

And on a personal note, I can't believe that this thread has been open for over a year now. Wild.

Posted by: @coracle

I do not believe she can play Aslan and get away with it.

What if her husband is also part of the deal? Meryl Streep is a big-time actress, and very experienced, but if part of that success is due to her husband's backing and enthusiastic co-operation, and if, as it seems to be the case, he, also is an actor & knows the ropes, perhaps that very closeness & learned ability to work in with each other is just what is wanted? If so, I am hoping for something truly magical to appear. Is there any technical reason why that might not ever be the case? No, I don't think that Meryl Streep could play Uncle Andrew, and, in any case, isn't it going to be Daniel Craig? The sort of character that Uncle Andrew is, should be flattered that the distinguished 007 actor would want to play him, anyway, when Uncle Andrew was something of a snob.  

@rachel In addition to using a British accent in The Iron Lady (for which she won an Oscar), Meryl Streep also used a British accent in The French Lieutenant’s Woman (for which she won a BAFTA and was Oscar nominated), Plenty, and Suffragette.

In a film called Evil Angels, way back in the 1980's, Meryl Streep had to adopt an Australian accent, to play the role of Lindy Chamberlain, who was imprisoned when she was falsely accused of killing her baby daughter, Azaria. These days, Lindy Chamberlain remarried & went to live in USA. 

Oh  she might get away with it for the average movie goer, but not for a lot of real Narnia lovers.