Heat oven to 350°F. Spray large cookie sheet with cooking spray. Remove dough from cans. Cut each loaf in half, making 4 small loaves. Place loaves seam side down, 3 inches apart, on cookie sheet. Cut 2 diagonal slashes (1/2-inch deep) with sharp knife on top of each loaf. Bake 22 to 26 minutes or until golden brown.
Meanwhile, pour soup into 2-quart saucepan. Add beef slices. Heat to boiling over medium heat. Reduce heat; simmer 10 minutes. Drain, reserving broth.
Cut loaves in half horizontally. Arrange 1/4 of the beef-onion mixture and 2 slices of the cheese on cut side of each bottom half. Drizzle cut side of each top half with reserved broth. Place top on each sandwich; press down slightly. Divide remaining broth among 4 small bowls or ramekins. Serve with sandwiches for dipping.