Mercenaries 3: No Limits was an unreleased video game that was suppose the be the squeal to Mercenaries 2: World In Flames. It was developed by Pandemic Studios before it shut down in 2009. There was also another Mercs game called Mercs Inc., which was a multiplayer based game which was released at the same time as Mercs 3
The only known thing about Mercs 3 is that it was likely set in Cuba, as shown on a video in the Mercs wiki, but that was it.
Why it was cancelled
The only for certain reason was that Pandemic Studios shut down by EA in 2009, thus ending development of the game