QTip #0002 - Use Siri to launch Google Maps instead of Apple Maps
Here is a quick video explaing how to use Siri on an iOS device to launch Google maps rather than Apple Maps - just use 'via transit' at the end of your question. Eg. "Siri, give me directions home - via transit"
That will launch a window in the app store that allows you to choose which map application to use for the directions your asking for.