Unity Register For One Interface Multiple Object and Tell Unity Where to Inject them

In the example below you have an interface implemented twice and injected on demand into two different client classes, just as you request. The trick is to use named registrations.

class Program
{
    static void Main(string[] args)
    {
        IUnityContainer container = new UnityContainer();
        container.RegisterType<IFoo, Foo1>("Foo1");
        container.RegisterType<IFoo, Foo2>("Foo2");

        container.RegisterType<Client1>(
            new InjectionConstructor(new ResolvedParameter<IFoo>("Foo1")));
        container.RegisterType<Client2>(
            new InjectionConstructor(new ResolvedParameter<IFoo>("Foo2")));

        Client1 client1 = container.Resolve<Client1>();
        Client2 client2 = container.Resolve<Client2>();
    }
}

public interface IFoo {  }
public class Foo1 : IFoo {  }
public class Foo2 : IFoo { }

public class Client1
{
    public Client1(IFoo foo) { }
}

public class Client2
{
    public Client2(IFoo foo) { }
}

This is most probably what you do wrong:

Container.RegisterType(forClass, uniquename, 
    new InjectionConstructor(
        new ResolvedParameter(dependencyService.To)));

You create a named registration for your concrete class. Instead you should have

Container.RegisterType(forClass, null, 
    new InjectionConstructor(
        new ResolvedParameter(dependencyService.To, uniquename)));