Place the venison, red wine, juniper berries, peppercorns and bay leaves in a large bowl. Leave in the refrigerator to marinate for several hours, preferably overnight.
Heat 1 tablespoon of vegetable oil in a large ovenproof casserole and sauté onion until translucent.
Meanwhile, remove venison from the marinade, retaining the marinade for later use. Pat the meat dry with kitchen paper. Mix together the flour, salt and pepper and coat venison with the mixture.
Preheat oven to 140 C.
Remove onions from the casserole. Add the venison to the casserole and brown in small batches (about 6 cubes at a time). Add more oil or a knob of butter if necessary. Once meat is browned, return all of the meat and onions back to the casserole and add the chopped carrots. Pour the reserved marinade over the meat and vegetables.
Put the lid on the casserole and cook in the preheated oven for 3 to 4 hours. The casserole is ready when the meat is tender and falls apart with a fork.