My recommendation is that you start with Bosch CAN 2.0 spec, and then move on to openXc, if you have access to a newer Ford vehicle, they provide you with details on how to leverage some CAN interfaces.
Another thing to note is that OBD is a standard, but the implementation of CAN is not, different vehicles will have CAN buses wired to different pins on the connector, and also multiple buses.
But like MD said, most of this information on the buses is proprietary, and you will have to do some reverse engineering.
I look forward to hearing more of your questions.
You don't send messages to a specific ECU, Can Message are sent to all modules on the bus (or all buses via a gateway). The question your really need to answer, is what messages does that particle ECU Listen for.
BOSCH CAN SPEC: