Brown buffalo roast on all sides in hot oil in a large ovenproof Dutch oven.
Combine water, vinegar, sugar, salt, and liquid smoke; pour over buffalo roast. Insert meat thermometer. Top with onion and celery.
Cover and bake at 275° until desired degree of doneness: about 1 1/2 hours or 140° (rare); about 2 hours or 160° (medium). Let roast stand 20 minutes before slicing. Transfer to a serving platter, and serve with Easy Barbecue Sauce.