Would Tom Hanks even do a Civil War film. He seems to be more into World War 2 films. Take a look at the credits for almost every historical mini series HBO has done in the last 15 years and you'll see Mr. Hanks has been an executive or associate producer for every one: Band of Brothers, From the Earth to the Moon, John Adams, the upcoming Pacific War series, etc etc. I know it's a pipe dream but damn if I don't think HBO/Playtone(Hanks production co.) would be the perfect fit for this project.
If you want to do a Civil War film why not ask HBO since they do more history shows than even the History Channel. Come to think of it I think the Food Network does more history shows than the History Channel.