Spray 4- to 5-quart slow cooker with cooking spray. Place onion in slow cooker. Place beef roast on onion. Sprinkle with garlic, chili powder, salt and pepper. Pour tomatoes, broth and wine over roast.
Cover; cook on Low heat setting 7 to 9 hours.
Remove roast to cutting board; cover to keep warm. Ladle cooking liquid into 2-quart saucepan; heat to boiling. In small bowl, combine cornstarch and water to form smooth paste; stir into boiling liquid. Cook and stir 1 minute or until thickened. Slice beef; serve with gravy.