Spray 3 1/2- to 4-quart slow cooker with cooking spray. In slow cooker, place turkey breast halves. Sprinkle with salt and pepper.
Cover; cook on Low heat setting 7 to 8 hours.
Remove turkey from slow cooker; cool slightly. Remove 2/3 cup juices from slow cooker; place in 1-quart saucepan. Add soup; mix well. Cook over medium heat about 5 minutes, stirring occasionally, until hot.
To serve, cut turkey into slices; place on bottom halves of buns. Pour gravy over turkey. Cover with top halves of buns. Serve sandwiches with cranberry sauce.