According to this Destructoid report, EA's to release a Total Payback DLC pack for Mercenaries 2 later this month, to include cheats, new playable characters and more.
Here's what you'll get:
Cheats: Infinite ammo, infinite health, and unlock all weapons, vehicles, and airstrikes Six new playable characters: Blanco, Fiona, Ewan, Eva, and more Cross-region co-op: Play multiplayer with friends from foreign countries
We're assuming this is free, in which case: awesome. Not sure why cross-region gameplay was in there from the start, but there we are.
It's out on October 13 for 360 and October 20 for PS3.