Selecting communication between microcontrollers at high temperature
If you choose CAN then the "best" micro is one with CAN built in (many have this, Coldfire MCF5225x is one example).

I2C or RS485/RS422 are good choices too, depending on the electrical characteristics of the situation (distance, noise, power). The rest comes down to the protocol you use for communicating - how to address messages, control flow, avoid collisions.

I'll wish you good luck finding a micro which will work at 180c, automotive spec tops out at 125c and I don't think even military spec improves drastically on that.

You need to start with layer 1 (electrical) to work out what the physical interface has to do, after that it's mostly a software issue on how you talk. These days, ethernet might even be a viable option if the micros have the space to run a modest OS.