Would doubled 2x12's suffice for a load bearing beam 16 feet long that holds roof truss in new england.

Sorry but no where near enough info to answer. Are you talking about a 16 beam supported only at each end which has trusses along it for the full 16'? This would be like a garage door opening, right?

Trusses typically don't need a bearing wall. What are you trying to accomplish? Parallel or across the trusses?