Not something I've done, but ultimately you'll need a RADIUS server that integrates with your Google directory. You could look at Fox Pass or Jump Cloud if you want something cloud based. Or as you said something like freeRADIUS which you'd then need to integrate with your Google directory. If you're doing WPA2-Enterprise then the certificate trust is between the wireless client and the RADIUS server (not the Meraki access point), and potentially also between the RADIUS server and the directory if that connection is secure too.