According to an interview with Kotaku:
Finally, Chilton and Chris Metzen, vice president of creative development at Blizzard, explained a new feature coming with the patch called "Raid Finder". The Raid Finder essentially operates like a dungeon finder, automating the search for fellow players on the hunt for a good raiding party. It will be built into the game's updated user interface when the patch hits, they said.
The Kotaku article doesn't call it a "cross-realm" raid finder, but I think it's safe to assume that it will be -- otherwise, it'll just be like the one that's in game now (you remember that one, right?). There's no more details on the interface or accompanying restrictions on the new raid finding, but expect that information to be discovered or announced soon.
Brace yourselves for what could be some of most exciting updates to the game recently with patch 4.3. Look at what's ahead: new item storage options, cross-realm raiding, cosmetic armor skinning and your chance to battle the mighty Deathwing -- from astride his back!