According to Empire...
From left to right, that's Matthew Mcfadyen as Athos, the quiet, brooding leader of the trio; Percy Jackson's Logan Lerman as would-be musketeer D'Artagnan, looking impossibly young and naive next to the others (no bad thing, that); Ray Stevenson as the hard drinking, hard living Porthos and Luke Evans as ladies' man / man of God Aramis.
The film, also starring Milla Jovovich, Orlando Bloom, and Logan Lerman, hits theaters October 14th next year!