It appears that your question is not about CAN or even OBD2, but whatever protocol the ELM327 chip presents over the USB. If I understand it right (and I very well may not), the ELM chip tries to make the OBD information more uniform despite differences between manufacturers. If so, they surely must document how to talk to their chip. Did you look around for the protocol.
It also seems like you have access to the raw CAN bus via the Microchip converter. In that case you need to know the OBD2 standard, and perhaps how your particular car handles some of the proprietary aspects. The official OBD2 standard may be expensive, but I expect there is a lot about it on the net anyway.