Google is everywhere!!! It will backup you when you are in lack of something. As we know Siri is subordinate in its part of the role. It's not that smart like google assistant. Here is the difference if you wanna know. Previously Google took many back seats for the IOS like Maps and Music’s. And now it's with Siri. So from now on IOS users easily find a way to catch up with Google Assistant.
They just added the latest version of Google Assistant app with IOS support will be available to make a shortcut in the home screen. And you can also program the app and it will start to listen to you. You have to say "Hey Siri, Hey Google" then you have to wait for a few seconds for the assistant to open and then you speak your command to Google.
So in this way you can get access to Google assistant through Siri. It is not the most desired solution but it's better than before. You can download it now for your IOS ( Click Here )