It's an entirely possible AAs will be "racing" at the same time as our car. That way it could be us against Mario and others. They could be in karts on tracks next to ours so looks like they're winning then we pull ahead and Mario says "Oh Nooo" like in the game.
The early concept art rendering shows a shot from our point of view in the car and Mario was seen in the car in front of us. Could be cool.
... Or they were just using characters as stand ins for guests in the concept art.
To me, making it seem like we're racing the real Mario characters would make it really feel like we're IN THE GAME and not just on a ride.