That's good then, you have lots of options to choose from.
You can consider the bus or train up to Santiago de Compostela (1 night), then head by train or bus or plane to either Burgos, Bilbao or San Sebastian, then train or bus again to Hendaye or/then Bayonne.
Or see about picking up a car in Santiago de Compostela and dropping it off in San Sebastian, spending a night on the road in between.
Or, take a direct Porto - Salamanca bus, spend the night, then take a Salamanca - Burgos or Leon connection, spend the night, then head to Bayonne (probably with a change in Vitoria or San Sebastian/Donostia).
Search each segment that you'd like individually and decide. Check both bus and train for each segment.
Personally, I would choose one of Santiago de Compostela or Salamanca for my first night, then either way Burgos for the 2nd, if using public transportation.
Check Renfe for trains and Internorte or ALSA for buses. Pesa runs San Sebastian - Bayonne buses.