We'll learn more about the game when EA actually, you know, announces it, but it's pretty self-explanatory: a garden simulator -- in THREE DEE. Like a real garden, but without that noisome sunlight! And also with a cartoon tanuki guiding you. Our garden doesn't do that. At least, we don't think so.
Update: An EA producer just showed the game, in which players unlock plants by completing photo-based goals. It'll be out alongside the 3DS, whenever that is released.