Recently iOS 6 was released and apple took away the most used Google maps application and they just replaced it with their own personal Apple maps, well that looked awesome but still lacked that awesomeness of Google maps, but few days ago Google came up with their brand new Google Maps app for iOS devices that rocked devices all over the world and people including me loved using that application as directions in Google maps are pretty much stable. But the thing Google maps were lacking was integration with Siri and using Siri to get directions in Google Maps.
But now people at jailbreak nation came up with an awesome idea or tweak what ever you can call that allows you to get directions in Google maps using Siri and that too without any jailbreak as we have no news about any jailbreak for iOS 6.
So now everytime you are searching for directions using Siri you just need to complete your sentence by adding a small phrase
"via transit" at the end that will automatically popup the Google Maps application and you will get the directions.
So like if you are asking Siri for directions like "Get direction to Portland airport" just add via transit at the end that makes "Get directions to Portland airport via transit" so makes sense. do check out the above video if you need some proper demo on how this thing works out.