Hello Richard M,
I am afraid that you are unable to execute a Linq query against more than one database simultaneously. Such support is not planned for the future yet.
Actually you could execute the query in parts on the server and finish it on the client later using Linq to Objects. For instance try to provide filters for both queries and execute them applying the ToList() method. Then combine the result collections in one query which will be executed on the client:
List<Class1> list1 = context1.Where(x => ...).ToList();
List<Class2> list2 = context2.Where(x => ...).ToList();
Hope that helps. If any other questions arise do not hesitate to contact us back.
All the best,
the Telerik team