I had previously done a short review about Apple Car play. One of my criticisms was that it wasn't possible to use text entry for destinations in maps and that Siri wasn't very good at voice entry of addresses.
I was wrong, you CAN pull up a keyboard.
Here are the steps:
1. Open Maps from the Car Play Screen
2. Press Destinations
3. Press the magnifying glass symbol for a search
4. Press the keyboard symbol on the right top.