As hinted in the design section, the first step in integrating SD-Branch with the Google Cloud Platform is to deploy at least one (or an HA pair) Virtual Gateway (vGW) in GCP. The complete process is documented in the Aruba Central Help Portal. Nevertheless, this document will describe the key steps.
Once that necessary step is taken care of, integrating the vGWs with the NCC service will enable the communication between the SD-WAN and Cloud environments.