CERZA at Lisieux is an excellent zoo which most resembles Whipsnade I guess. It consists almost entirely of large paddock type enclosures with very little indoor viewing. There is a train through a large wooded part of the zoo, but you can walk around that area if you want too. I would definitely recommend it if you are in Caen which is about half an hour away.
If it helps a little, I had a good conversation with a French keeper at Africa Alive who had worked all over the world in her job (she had even looked after Northern White Rhinos!) and she recommended CERZA as an excellent place to visit.
Thanks for the info, it's always good to hear the views of people who have visited a lot of zoos. I will certainly pay the zoo a visit while I'm there.
Cerza is a very decent zoo; it feels very much like an English place, with enclosures designed more for the animals than the visitors. It doesn't have the panache of the best French zoos, but it is certainly worth a visit. The highlight is possibly the excellent spectacled bear enclosure, but Indian rhinos are done well too.
Also in Normandy, I'd recommend the zoo at Champrepus. This is quite small, and has little that is interesting species-wise, but it is beautifully done, with great planting and a very nice feel. Nearby, Jurques is another zoo with a very british feel to it - a bit like Banham perhaps. Decent collection. Some nice housing, some pretty basic. Money clearly not available in abundance, but worth seeing.
Surprisingly good is Alligator Bay, near Mont St Michael (Parc animalier - alligator-bay - Crocodiles, tortues...). The name might not suggest zoological excellence, but there is a decent reptile collection and an excellent crocodillian collection - there's something really rather impressive about seeing 30 or 40 Nile crocodiles together.