You're going to have to define your requirements a little more clearly than stating "I want one single orchestration layer". What does that mean, exactly? Are you just asking for a way to view and manage clusters across both sites? Something more? If so, what?
A single vCenter Server can manage all three clusters. But note that your requirements may make this impossible. if for instance you need DR with SRM than you need 2 vCenter instances. So as mentioned above, you need to be a bit more specific.