How to handle connection pooling for massive multi-tenancy/multi-schema environment
You have 2000 schemas spread across 50 servers...I don't think there's a connection pooler that exists to handle that type of situation.  You're going to have to roll your own in application code, I believe.

I'd really step back and take a look at your architecture.  What happens if you double the number of customers?  Triple it?  This type of design seems seriously unmanageable and difficult to scale to new levels of business. 

HTH,
Dave Sisk