In 10-inch skillet, melt butter over medium heat. Add pork roast; cook 3 to 4 minutes on each side or until browned.
Into 3 1/2- to 4-quart slow cooker, pour sweet-and-sour sauce. Add pork, broth and drained pineapple.
Cover; cook on Low heat setting 4 hours 30 minutes to 5 hours.
About 15 minutes before serving, in small bowl, mix water and cornstarch until smooth. Remove pork from slow cooker; place on cutting board or serving platter. Stir cornstarch mixture into juices in slow cooker. Return pork to slow cooker. Increase heat setting to High; cover and cook 10 minutes or until sauce has slightly thickened. Cut pork into slices; serve with sauce.