I don't use Google maps for navigating, but "Car mode" always open Google Maps when you select "Navigate" from "Car mode". Who do one change that (I use Sygic, while I wait for Nokia Here :-)
Driving Mode features on Samsung Galaxy series like Galaxy S2, Galaxy S3, Galaxy Note 2 and others, notifies you the incoming call and notifications by reading it out. Learn How to Enable Driving Mode on Samsung Galaxy series by doing as follows:
1. Open Setting app
2. Go to Language and Input
3. Tap on "Text to Speech output"
4. Make sure the "Driving Mode" is checked and activated
You also can choose what types of notifications you want to be notified about while driving. To do so, you just need to tap on the "Driving Mode" and enter to the Driving Mode Setting.