Supporting both GearVR and GoogleVR in single .APK ?

Is it possible to support both GearVR and GoogleVR (previously Cardboard) in a single .APK build?
Or do I have to create two separate APK’s and release these as two separate apps on the Google Play Store?

If Yes: Would love to be referenced an example for having a custom pre-VR window (for selecting VR version, possibility for adding more controls like settings etc). This before you attach your mobile to the headset.

You can add multiple different VR in a single game, it will use the first configured available see the documentation VR overview.