when raspberry pi 3 handles 10 Thousand connection
Very, very unlikely. If each connection were generating 1 KB/s of traffic, that's 10 MB/s, which is just within the 12 MB/s theoretical upper limit of the 100 Mbps ethernet NIC.
But I don't see how a 4 x 1.2 Ghz processor is going to be able to do much with that volume of information, besides maybe turn it around. That's without starting to think about the overhead of just juggling all the connections.
Of course, 1 KB/s may be a high average. In any case you need to look closer at your requirements but if you are really talking about 10,000 concurrent connections, no matter what they are doing, a Pi 3 is not an appropriate solution.