Architectural pattern for importing data from disparate sources

So I have a couple of classes I am trying to design for different services that have different types of connections. I'm trying to figure out the best pattern to follow for designing these. The services connections can be different types (oauth, saml, etc.) and their return types can be different (json, xml, etc.) but I'm trying to hook up a core interface to define how to communicate with them. Basically I have individual classes that represent connections and then individual classes that represent the mappers between the returned data (which could be a number of formats) and my persistence layer. I need some way to communicate between my service and the external service so I need some sort of controller to do that mapping. Are there any best practices or patterns I could follow to help in the creation of this class? Right now I'm having trouble creating a polymorphic connection object and keeping its concerns separated from my controller object.