The film will tell the story of the three Americans who stopped a terrorist on a train bound for Paris, according to The Hollywood Reporter.
Paul-Mikel Williams, Max Ivutin, Bryce Gheisa, Cole Eichenberger, and William Jennings will play younger versions of the Sadler, Skarlatos and Stone.
Jenna Fischer, Judy Greer, and Ray Corasani will also join the real-life heroes in the film.
The casting move is similar to Eastwood's "Gran Torino," which featured an almost unknown cast outside of Eastwood, who also starred in the movie.
Eastwood will produce with Tim Moore, Kristina Rivera and Jessica Meier.