Once you have Google Maps downloaded (includes Nav), click on and address that would normally open a map (like and address section in one of your contacts). It will ask if you want to open in Google Maps or Bing , select Google and check the "Use as default" button. This will default your maps.
The phone comes pre-installed with a "Voice Search" app. Add that to your desktop for 1-click access to voice commands from Google, i.e. "Navigate to Starbucks". If you use that, and for some reason you get a choice again of Google Nav and VZW Nav, just select Google and check "default" again.
It works nicely for me.