If it's cycling you want to do... and lots of it... why not The Netherlands? It's Europe's best country to ride. Belgium is great if you want to see the classics, and try cobblestones and some hills. And throw in some nice historical cities . The weather in May can be wet though.
France is a good option too. I love Brittany. Or go more south to the Provence. Some great cycling there too.
Lot's of cyclist from Belgium, Holland, Germany go to majorca (Spain) in may because of the weather but not for the views.