CBS Films is betting on "Gambit."
Oscar-winners Joel and Ethan Coen ("No Country for Old Men," "True Grit") wrote the script. Michael Hoffman ("The Last Station") is directing.
Mike Lobell is producing with Crime Scene Pictures partners Adam Ripp and Rob Paris, who are financing. Rizal Risjad is executive producer.
It's about an art curator, played by Firth, who tries to con a wealthy collector into buying a fake Monet. As part of the gambit, he recruits a steer roper from Texas, PJ Puznowski, played by Diaz, to pretend to be a woman whose grandfather liberated the painting after World War II.
CAA set up financing for the project. Attorney Philip Elway negotiated the deal with CBS Films.
FilmNation Entertainment is handling international sales.
The film begins shooting in London this May.