Place bison pot roast in a large zip lock bag with flour, garlic, salt and pepper. Shake well to coat and allow to rest for 10 minutes.
Place a heavy bottomed pan on the stove and preheat for 10 minutes on medium low.
Add vegetable oil and brown the roast well on the first side for 7 minutes and the second side for 5 minutes. Remove and set aside on a platter.
Add onions to same skillet and saute until soft and clear, about 9 minutes. Add carrots and celery and cook for an additional 11 minutes. For best flavor the vegetables should caramelize.
Add one heaping tablespoon of tomato paste and continue to saute for an additional 2 minutes.
Add beef stock or stock/wine mixture. Return roast to pan, bring liquid to a boil and immediately reduce to a simmer.
Cover and cook on lowest stove top setting for 7 hours OR Set oven temp to 180°F and cook in covered heavy casserole for 8 hours OR Transfer to slow cooker and cook on low for 8 hours.
When the meat is fork tender, remove roast and let rest for 10 minutes before slicing.