Who should play the role of the slave in the new Quentin Tarantino's movie?

It was announced that QT was screepting a new movie where a former slave would get trained by a German bounty hunter so he could get his wife back from the slave master (leornardo Di caprio). Jamie Foxx I believed nailed the part, was it a good choice as Will Smith was the favorite! what about Chewetel Ejiofor (2012), Idris Elba (thor), Anthony Mckie (hurt locker)?