How to use Siri to get Google Maps directions
The best part of the trick is that it will work on any iOS device that has both Siri and Google Maps, and doesn't require jailbreaking. All you have to do is tag your directions request to Siri with the phrase "via transit", and Google Maps will pop up as an option to give you those directions, because Apple Maps can't. Once you're in, you can then switch the mode of travel to driving or walking if need be.
How's that for easy?
source: Cult of Mac