Although many people have now downloaded the new Google Maps App for iOS 6, they are still finding that, when they use SIRI to ask for directions, by default the Apple Maps App is being brought up. There is a way for you to set the Maps App to Google by default when using SIRI and it does not require any hacking or jailbreaking.
When you ask SIRI for directions, simply add “via transit” at the end of your voice command, for example, “Give me directions for work via transit”. This will then bypass Apple Maps and take you to a screen that lets you select Google Maps. Simply tap on it and Google Maps will open with your destination already populated. Because the app thinks you are looking for public transit directions, this will be the default route so make sure to change it to walking or car directions if that is what you are looking for. Tap on your preferred selection and your directions will come up. While this is not exactly a hands free solution, if you want to use SIRI for directions and you don’t want to use Apple Maps this is your best option.
For those of you that have jailbroken devices, get the MapsOpener tweak from Cydia and set your default Maps App to Google. This will then open Google for any maps links except for those in you Contacts list.