The actor was supposed to star opposite Reese Witherspoon. Twentieth Century Fox has confirmed Cooper's departure. They say it had to due with scheduling conflicts with The Hangover 2.
Director McG (Terminator Salvation) is in negotiations to direct this project. It is set to start shooting in July. Todd Philips is not planning on shooting The Hangover 2 until the fall. Cooper could do both films, but apparently "the actor had creative concerns regarding the project."
This Means War focuses on two spying best friends whose relationship comes undone when they fall in love with the same woman (Witherspoon).
Fox hasn't said what they plan to do to replace the actor as the script was at the top of their priority list.