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

dmesg

CAN device driver interface
mcp251x spi0.0 can0: MCP2515 successfully initialized.

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

apt install can-utils

Host 1

candump can0

Host 2

cansend can0 123#DEADBEEF

Schematic