The PiCAN is a reimplementation of the interface found here.

Append the following to boot/config.txt and reboot.

dtparam=spi=on
dtoverlay=mcp2515-can0,oscillator=16000000,interrupt=25
dtoverlay=spi-bcm2835

ip link set can0 up type can bitrate 250000
ip link set can0 txqueuelen 1024
ip -s -d link show can0

Schematic