Serebii.net has a few more details on PokéPark 2: Beyond the World, including details on how the Pokémon you can play as differ from each other.
PokéPark 2 lets you play as Pikachu, Snivy, Tepig and Oshawott. Pikachu is the most balanced of the lot and doesn’t appear to have any unique abilities. Snivy can increase his jump height by using the Leaf Tornado move, which allows him to reach areas that other Pokémon can’t easily access.
Tepig can use Flame Charge to destroy boulders scattered around different areas and is the strongest of the four. Finally, Oshawott is the only one of the four that can swim in water areas.