From Variety:
Three more cast members have been added to X-Men Origins: Wolverine: Ryan Reynolds as Deadpool, Taylor (Friday Night Lights) Kitsch as Gambit and hip-hop musician will.i.am as John Wraith.
Marvel has been eyeing the possibility of casting Reynolds as Deadpool, an assassin with self-healing powers, for some time with the idea of spinning off the character into his own film series should the character prove popular among moviegoers.
Fox and Marvel have also long wanted to add the card-throwing character of Gambit to the "X-Men" franchise but could never find a way to give him enough screen time among the many other mutants that have appeared in each film.