*We are spending one day in each of these towns while on a cruise in November. Do either of these towns have Hop On Hop Of Buses? What fun things can we do in such a short amount of time? *
Weather in November will be kind of chilly, although you never know as weather in northern Spain is quite unpredictable. In Bilbao you´ll be docking at Getxo, where I live, which is 9 miles from Bilbao city center. Yes, Bilbao offers a Hop On Hop Off bus, that will allow you to enjoy most of the city´s attractions, with the impressive and spectacular Guggenheim museum as the most important. It has a lovely, beautiful old quarter, full of pintxos bars and a great atmosphere. Also, a 1915 funicular train to Artxanda hill for the best views of the city, the Azkuna Zentroa, the Gran Vía...and a wonderful gastronomy!
I don't think A Coruña has hop-on / hop-off buses, but the cruise terminal is very close to the city center so it should not be an issue. A day is plenty of time to explore the attractive city center and make your way towards the impressive lighthouse (Hercules Tower).
Expect rain, the climate there is worse than Bilbao's.
The historic center of Bilbao, the Casco Viejo, is relatively large and non-touristy. You can spend a lot of time just wandering around there. I enjoyed the longish walk over there from the Guggenheim, but there are trams if you don't want to do that much walking or run into bad weather.