Chambers will play Barry Allen (the Flash), the superhero around whom the film centers and who is, to a certain extent, responsible for shaping the world of Flashpoint. McKidd stars as the Batman of the Flashpoint Universe, while Kevin Conroy will return as Bruce Wayne in the sections set in the main DC Universe that reportedly bookend the film.
Source (including image): ComicBook
Also reported by TV Guide
Bluray.com has an article about the release of the Justice League: The Flashpoint Paradox DVD here