if you simply want to read the CAN, I would recommend just buying something like a NeoVI which is sold by intrepid control systems. (Best tool I have found) It will read and send any messages you want and you can set up the software to interpret the messages in a matter of minutes. If you want to actually use the data to perform a function on you PIC, microchip has a lot of useful documents on their site for doing CAN. It explains the protocol and some example circuits both using the on Chip can and a stand alone IC. I must warn you CAN is a pretty complicated protocol.