I haven't looked at the squad rosters yet, so it's hard to make any well-informed predictions, but I'll go ahead and do it anyway...
Groups A, B, and D look pretty easy to call. I'd have to call Japan, Cuba, and the Dominican the favorites. In Group C, Italy has to be just "happy to be here." Canada and Venezuela are certainly capable of leaving the USA with egg on our faces again, depending on the rosters they assemble. Tom Singer's prediction for USA:
P Joey Devine, J.J. Putz, Brian Fuentes, Bobby Jenks, Mike Gonzalez, Brad Lidge, Cliff Lee, Joe Nathan, Jake Peavy, Scot Shields, Huston Street, Roy Oswalt, Mike Mussina, Joe Saunders
C Joe Mauer, A.J. Pierzynski, Jason Varitek
IF Derek Jeter, Chipper Jones, Ryan Howard, Alex Rodriguez, Ryan Zimmerman, Chase Utley, Michael Young, B.J. Upton (he's an outfielder now, though)
OF Curtis Granderson, Raul Ibanez, Matt Holliday, Vernon Wells, Ryan Braun
C.C. Sabathia wants to play, but since he's a free agent, he doesn't know if he'll be allowed to, and I didn't see anything about Tim Lincecum or Roy Halladay. Cliff Lee, Jake Peavy, Roy Oswalt, and Mike Mussina (with Saunders the backup) are a decent rotation.
I'm not thrilled with that outfield. I'll feel better if they move Upton to CF and bring in Dustin Pedroia, Ian Kinsler, or Dan Uggla. J.D. Drew and Carlos Quentin are beasts, if they're healthy; I might go with Grady Sizemore or Josh Hamilton for some more boom-and-pow. I don't know if there's any cover for Howard at 1B; Mark Teixeira is another free agent who can't commit to the WBC, but I don't see Prince Fielder or Lance Berkman mentioned anywhere (maybe they're just not interested). I doubt the Yankees or the Red Sox will allow their entire rosters to play in the WBC, so Team USA might have to choose who to invite to the team. Personally, I'd rather play A-Rod at SS and take Johnny Damon instead of Derek Jeter; and take Jonathan Papelbon instead of Jason Varitek (then get Ryan Doumit or Chris Iannetta to back up Mauer at Catcher).