SQL Server: Database integration and synchronization
If your update/insert always happens on a single one of the n databases AND you read a low number of rows on each request, you can use Linked Servers and Distributed Partitioned Views (DPV) to create the illusion of a single database: http://technet.microsoft.com/en-us/library/ms188299(v=sql.105).aspx. This can be done without introducing the complexity of replication.

DPV have several limitations and may give you poor performance if you are not careful. Without knowing more details of the queries you want to run - I can only advise that you try it and see if solves your problem.