How do I make Google Maps my default Maps app?
It's not possible to make the Google Maps app the default maps application on any device running iOS 6 or higher. Even with the stand-alone Google Maps app installed, iOS 6 will default to Apple Maps when a link is clicked or Siri is asked for directions.
There is a tweak called MapsOpener for jailbroken devices. When installed, this tweak will allow your device to access Google Maps when a link is accessed within a browser, but does not offer Siri integration.