I spent two days biking and kayaking in the Loire Valley, and it was the highlight of my trip to France. I pre-arranged my travel with Loire Velo Nature: http://www.loirevelonature.com/ who had amazing customer service.
I took the train from Paris to Tours. At Tours, I left my luggage with Hotel L'Europe, which was located right across the train station. They only charge 2euros a day for left luggage, and you don't even need to be a guest. Then I picked up my bicycle at the Best Western hotel, which is where Loire Velo Nature has a pick-up location. I bicycled about 14km to Savonnières, where somebody from Loire Velo Nature picked up my bicycle, and gave me a kayak. Then I kayaked about 1kkm to Bréhémont, the main store of Loire Velo Nature, and returned my kayak. I stayed one night at a bed and breakfast in Bréhémont run by Loire Velo Nature's owner, Celine. The next day, I got back on the bike and biked back to Tours, stopping by 3 chateaus along the way (~40km). Then I stayed at Hotel L'Europe and went back to Paris the next morning.
The bicycle route was very smooth and it's a great way to see the countryside. My only issue is that there's no place to fill up on water along the way, so I was very dehydrated by the time I got to Savonnières. Bring more water! The kayak trip was absolutely amazing. The Loire is definitely the cleanest river I've ever been on. I only saw one piece of garbage (a water bottle) the whole time I was on the river, so I picked it up myself and threw it in a trash bin later. I saw many birds and fish, and it was incredibly peaceful and beautiful.
I highly recommend this kind of trip to experience the Loire Valley, and also highly recommend Loire Velo Nature to help you arrange the pickups and dropoffs.