I just so happen to know a thing or two about Azure Dynamics DMOC controllers. Which controller are you using: 445, 645 gen1, 645 gen2? This will make a difference. I know something about all of them but their CANBus programming is totally different between the three.
Now, you seem to have a dash display which expects J1939 PID messages from an internal combustion engine (ICE) engine control unit (ECU). This is not as hard as it seems. A bunch of standard PID messages are detailed at this wikipedia page: http://en.wikipedia.org/wiki/OBD-II_PIDs
The gist of how PID works is this: A device sends a request to the ECU for a certain piece of data. This request is sent to the ECU broadcast address which is generally something like 0x7DF. It responds on a different but related address with the info you requested. This is all explained on the page I linked to. What you'd do, in order to show data on the dash display, is pretend to be the ECU. When the display asks for a certain piece of data (like, say, the fuel level) you receive the message and send back the fuel level in the proper format. You will have to get this data by processing frames from the DMOC motor controller. So, the arduino board will be a shim in between the two devices. This can be done with one canbus line or you could use both. It's up to you.
This is all quite possible with an Arduino board and some extra canbus goodies. I worked on canbus libraries that work on both the 8 bit Arduino mega type boards (well, it was a Macchina but that's an Arduino Mega clone with canbus) and on the Due. So, I can vouch that canbus works on both boards. I'll be around if you run into trouble.