I've used I2C and CAN.

I2C is electrically far more fragile than CAN. CAN is robust against all sorts of electrical faults. While you might not be able to transmit data, you won't fry the controller, and once the fault is removed it comes back.

I2C is often more tolerant of unexpected traffic on the bus. There are far too many ECUs that will put a vehicle into limp mode (limit speed drastically) if they detect unexpected CAN traffic, even traffic not directed to them. Protocol-wise I2C is significantly simpler to get right.