From all directions you can easily get to the Lahn valley either by car, train or bus. The station Feudingen is located only 9 km below the Lahn source, right at the Lahn hiking trail and at the Lahn bicycle route. From there you can easily get to the entire Lahn valley by train, e.g. from Marburg and Gießen (IC stations) and from Limburg and Koblenz (ICE). The German Rail will even facilitate your canoe tour planning, too.
You will find detailed and latest information around travelling by train as well as tickets (also for bicycles and reservations) here. You can also use the country ticket „Schöner Tag Ticket NRW“, „Hessenticket“ and „Rheinland-Pfalz-Ticket“ within the Lahn valley. Details concerning the country tickets here.