I did a few little tests last night, inspired by the descriptions on the character selection screen, for example “Killer wheels”, “turbo squawk”, “old reliable” etc.
The wording and the fact that they are there at all made me wonder if there ARE some slight differences between characters. Things like maybe the shark nudges other racers harder when he bumps into them, or the pelican gets a slightly better boost on the turbo powerup or something.
So I went into two player mode and did a bunch of controlled experiments, carefully lining different characters up and hitting accelerate or brake or turn at the same time.
Anyway, long story short I couldn’t find any noticeable differences. Though, to be fair, they were not completely comprehensive tests – I didn’t try every character against every other in every situation, so maybe there was something I missed.
The other possibility is that, to make it more fair, they nerfed all the bonuses for two player mode, and the different stats or abilities only come through on single player.
If I were truly obsessive about this I would try to find out how to edit the demo files, and change the characters to see if they become unsynced. But… I don’t really care THAT much!