In a small skillet, saute onion in butter until tender. In a large bowl, combine the bread cubes, celery salt, garlic powder, salt, pepper and onion mixture; toss to mix evenly. Add egg; toss to coat bread cubes. Roll into ten 1-1/4-in. balls. Wrap a bacon strip around each ball. Secure with a toothpick. Repeat with remaining ingredients., In a large skillet, cook bacon roll-ups on all sides over medium heat for 18 minutes or until bacon is crisp and a thermometer inserted into stuffing reads at least 160°. Drain on paper towels.