Gaming: C#-C++ network communication

Question

Hi,

I am to write a C# game serrver, which would communicate with a C++ client. It should be used just for the administration communication (not during the game itself, just administrating different game rooms, users, tournaments ...), however there should be many thousands concurrent users online, security is very important, and scalibility and reliability too.

I am not quite sure, what kind of communication technology I should use.

WCF (I would prefer this one, however no idea, if appropriate)?
Web Services?
TCP Sockets?
Amazon SQS?
MSMQ?
Just REST using JSON?
Any other ideas?

The problem is of course, that the development should not last for ever :).

Thanx very much for any insights.
alvar