I have a [Sparkfun shield][1] [1]: https://www.sparkfun.com/products/13262 that does CAN and GPS. The end-goal is to have an Electron replace the Photon that’s currently serving the development role, so I can start the vehicle, read telemetry data and (as a bonus) locate the truck if it’s ever stolen.
If I’m understanding you correctly, it seems like I’m using a drill to open a lock. I feel like I should be approaching this differently.
If you want CAN too you might also want to talk to @jvanier who has created a Photon & Electron CAN module, formerly called CANdlestick but now being Carloop.
And maybe he can give some background on the GPS extension mentioned on their site too 
Thanks ScruffR, I’ll give it a look!
What’s the code to communicate Spark Core back to Arduino?
Do you need that for yourself or in order to suggest a solution for Daley’s problem?
If the former, try to outline what exactly you need.
But in general the communication from Particle to Arduino works just the same as Arduino to Particle.
You can also use Carloop with the Redbear Duo if you want Bluetooth (BLE) + CAN capability. Happy to answer any questions re: Carloop as well.