Cut top fourth off of sourdough loaf and carefully hollow out the bottom, leaving a 1-in. shell. Combine the cheeses, mayonnaise, chopped onion, crumbled bacon and minced garlic. Spoon the dip into bread bowl. Replace top. Place on an ungreased baking sheet. Bake at 350 degrees for 1 hour or until heated through. Serve hot with crackers and/or baguette slices.