I think that CAN-BUS Shield I linked has an Arduino library on Github, complete with examples you can reference, when you're ready for that step. You mention that most of your dev experience is in ...

Once it detects that he is trying to roll the windows up or down, the Arduino issues the proper window control commands to the bus, and his wish is the car’s command.

After all, CAN is a multi master protocol, meaning multiple devices can take the initiative to start talking. You will have collisions on the bus which need to be handled. Report comment ...