I have not used the ElecFreaks CAN BUS Shield. I have used the seeedstudio CAN-BUS_Shield_V1.2 - the only problem I had was the CANH and CANL on the 9 pin out did not match the pin out on my other canbus kit. It is worth checking your pin out.
I find a USB-CAN dongle for a PC is very useful for debugging Canbus projects.