We did bourg d’oisans in June and it was really really good, I’d go back .
Used http://promptcc.com/ for bike hire and accomodation.
Loads of routes available from medium to massive.
Alp d’Huez
Col de La Sarenne
Les deux alpes
Col de la croix de fer
Col du glandon
Col du Galibier via lauteret (You will need lights assuming it’s open Tunnel or snow!)
And the easy but spectacular balcon d’Auris
Croix de fer was a great climb. Lautaret was shut but the road is busy and unpleasant.
There is a booklet you can download somewhere with all the routes. Much quieter than the maurienne valley.
We also saw bardet training on alp d’Huez.
Just don’t scratch the bike.