Here’s an Istanbul region map, including Bandirma, Bursa, İznik (Nicaea) and Yalova.
Here’s the Turkish General Directorate of Highways’ map of the Istanbul region’s highways.
Fast catamaran ferries carry cars and passengers from Istanbulacross the Sea of Marmara to Bandirma, whence you can continue to Aegean Turkey by bus or train; and Yalova, whence you can continue by minibus to İznik, or by minibus or bus to Bursa.