Upgrading from sync with nav to sync 3
 

I would think you could but it wont be easy or cheap, and half the function might not work. Best bet would be to start look at wiring diagrams of both your current nav and the diagrams for the car with the sync 3 you would want to be putting in your car. I have no doubt you could get it powered on and get sound working. However, I think they use different communication methods so that would be where you start to run into issues.