Episode #13: I2C and P82B715
I see what you mean. I just googled "Arduino CAN bus" and his site came up. I didn't look at his other stuff until you mentioned it. There is a typo in one of the programs that stops it compiling, but you shouldn't have any problem fixing it.
Some of the ebay listings say the MCP2515 modules are Raspberry Pi compatible, but as they come I don't think that's the case, especially if you want to use it in a mixed 5V/3.3V project. There is a tutorial online where somebody has physicaly hacked the module by soldering in a resistance bridge to allow 3.3V to 5V working, but it looks a bit of a mess and if things get that far (and we need R Pi capability) I will probably be looking to build something from scratch. There are also R Pi CAN hats available.