Ok, just to clarify... the CAN bus protocol can not be used to control throttle, brakes or steering. Critical stuff like that must be feedback driven.
Most manufacturers have their own communication protocol (some on top of the CAN bus). Probably the most researched and hacked bus out there is BMW's I-BUS (Used in MINI, BMW and Range Rover) [1].
You can however flash the ECU through most CAN buses (not in the protocol, but info about it can be found for most cars). And from there, one can interfere with the throttle.