I just might have found it. There is another resource called "HubVirtualNetworkConnection", this might be it, I still need to test.
But I have to say, that the naming is a bit unlucky as everything else (unless there's another one I missed) related to VirtualWans is called "Virtual..." But not the HubVirtualNetworkConnection.
In my opinion, this class should have been called "VirtualHubVirtualNetworkConnection" to be consistent. (I see that there are a lot "virtual" in this name, but I did not invent the underlaying resources' names...)