From WENN.com

An insider close to the top secret sequel developments tells Life & Style magazine that director Todd Phillips will shoot much of the new film in Los Angeles and Las Vegas before taking castmates Bradley Cooper, Ed Helms and Zach Galifianakis south of the border into Mexico.

The two previous comedies were set in Las Vegas and Thailand.

The Hangover 3 is scheduled to hit cinemas in May, 2013.