Cut rabbit in serving-sized pieces. Wash, scrape, and soak in salted cold water for 1 hour. Drain and dry. In a glass or pottery bowl mix together the wine, vinegar, salt, pepper, bay leaf, chopped onions, and pickling spice. Add the rabbit and let marinate in the refirgerator for 3 days. Turn the pieces occasinally. Drain the rabbit; strain and reserve the marinade. Dry the rabbit with paper towels and roll in flour. Melt butter in a Dutch oven or deep heavy skillet; brown the rabbit and sliced onions in it. Pour off fat and add sugar and 1-1/2 cups marinade. Cover and cook over low heat 1-1/2 hours or until rabbit is tender. Turn the pieces occasionally and add more marinade if needed. Taste for seasoning. Mix the sour cream into the gravy just before serving.