Querying GKE config parameters via Rancher API

I recently created a thread about creating GKE clusters using Rancher API somewhere in this forum. So now that I can trigger a GKE cluster creation action from NodeJS via Rancher API, I would like to be able to fill up the requests with some GKE parameters such as machineType, zone, etc. In the Rancher UI, when creating a GKE cluster, dropdown boxes are presented to allow selection of machine types and zones currently available on GKE. I was wondering if the Rancher API exposes some functions to allow querying of GKE-specific information such as these, or are we supposed to go directly Google Cloud API to retrieve the data?