As mentioned, the WPILib CAN VIs are customized for FRC and so is the Jag firmware. These customizations are largely for a safety heartbeat mechanism, but also take care of bridging the CAN traffic over either enet or serial.
Perhaps
http://www.ti.com/lit/ug/spmu065b/spmu065b.pdf or
www.luminarymicro.com/jaguar will be useful.
Greg McKaskle