Ok hear me out. Ledger's joker can't be immitated. A lot of people think he paved the way for how joker will be portrayed in the future. I think that's crazy talk. He did an amazing job and then he died. The last thing you want is for the next portrayal to try and immitate ledger's performance. You want something completely different and the way to be different is by immitating the comic book version. Don't limit your options to who can both look and act the Parr. Go with CGI and use facial motion capture. He has to look 100% real. Who should play him? Mark hammil from the cartoons and video games. He is perfect. Watch footage of him doing his voice overs. He fan do it better than ledger. But it would take CGI to make him look like the comic book. I'd not mark than just pick an actor who can act the part but don't limit our options to people who look the part. Use CGI facial motion capture to make him look perfectly like the comic book.