We followed the Eurovelo 6 bicycle route (http://www.eurovelo.com/en/eurovelos/eurovelo-6). Fortunately Europe has great bicycle infrastructure so we were able to stay on dedicated cycle paths or at least bike lanes the majority of the time. In the instances where we did end up sharing the road with cars, it was not an issue, European drivers are in general very cycle friendly. (Especially in contrast with New Zealand which was frankly terrifying.)

Awesome, thanks!

@kevin488 The Adventure Cycling Association is the de facto source for bike touring routes and maps: https://www.adventurecycling.org/routes-and-maps/