XDA Developers has obviously figured out a way to get Google Assistant to work on all Android phones, not just Google Pixel.

Google Assistant to mobiles with 7.0
The requirement is that the mobile phone is already running Android Nougat, you have Google Apps version or later and bearing on Android fiddling, but it is clear: you have already installed the Android 7.0 you know what you’re doing anyway.

Have Nougat is the dog easily. You can choose to manually edit a build.prop file, or download a zip file containing the required for automatic flashing.

Do such things at your own risk. Techulagam accepts no responsibility for errors with the device or machine you are flashing with.