Originally Posted by twowheels
Correct... before Siri.
Oh? Only thing that I know how to do is to launch the app with Siri. You can't say to navigate to an address and have it use Google Maps, only Apple Maps. You can use the microphone button on the keyboard for entering an address, but that's not really Siri.
Just add "via transit" to the end of your command, and pick Google maps from the list. Google's your friend.