I'm betting it's a second-party game. Squeenix have stated that they don't have anything in development for the Wii aside from the FF:CC games and Chocobo's Dungeon, Konami seems content to keep its Playstation-line mostly-exclusivity, and Namco-Bandai already has two Wii games announced.
Now, a big surprise would be if it were a Capcom game...
"'Casual games' are something the 'Game Industry' invented to explain away the Wii success instead of actually listening or looking at what Nintendo did. There is no 'casual strategy' from Nintendo. 'Accessible strategy', yes, but ‘casual gamers’ is just the 'Game Industry''s polite way of saying what they feel: 'retarded gamers'."
-Sean Malstrom