The stars join Melanie Laurent and Jesse Eisenberg on the cast, Variety reports.
Ruffalo is expected to play an FBI agent whose team becomes embroiled in a battle of wits with a group of magicians who use their shows to raid banks and then implicate their audiences. Seyfried will play a master technician.
Colin Firth, Sacha Baron Cohen and Jim Carrey were reportedly approached for leads in the film.
Louis Leterrier will be directing from a script by Edward Ricourt and Prince of Persia: Sands of Time writer Boaz Yakin.
Clash of the Titans director Leterrier dropped out of the sequel to the mythological battle film last year.
Ruffalo is currently working on Joss Whedon's The Avengers where he will take on the role of the Incredible Hulk.