I biked extensively on the EuroVelo routes last year. Through France, Italy, Scotland, etc. If I would need to pick one of the ones I biked, I would pick the EV4 from Roscoff to Calais. The landscape is absolutely stunning, specially in the first part. It is hilly, but not to the extend that it would be super hard. I'm personally not a big fan of biking on canals and I was glad to arrive on the coast after my time at the Vélodysée. There are not so many dedicated bike roads, but the streets are small and the french drivers are very courteous.
I took the ferry to Dover from Calais, but I believe the following stretches into Belgium and the Netherlands are quite enjoyable as well.
If you're interested, I wrote a little summary of my time at the EuroVelo 4, with accommodations and the routes I've taken: staunchy.com/routes/eurovelo-4 (sorry, not allowed to link)