Does anyone know if I can use Siri to make a phone call using Google Voice? Either that or place a call with the phone app using my Google Voice number.

I ported my main number out to Google Voice. I want to be able to make hands-free phone calls from my main phone number on Google Voice, instead of the random phone number I have assigned to my iPhone. Using "Hey Siri" opens the iPhone app, so does Google Assistant.
This depends on Google integrating their app with Siri as since iOS 10, developers can make their apps work with Siri using Siri Kit. So it’s up to a Google to do it, in the meantime, this isn’t possible.