The entertainment world is filled with extraordinary stories of musical power-couples, but few match the beguiling true-life tale of Natalie MacMaster and Donnell Leahy. Known as Canada’s reigning stars of Celtic music, the two musicians’ combined album sales exceed one million; they sell out performing arts centers across North America, and their enthusiastic traditional folk music loving fan base (which boasts Shania Twain and The Chieftains) stretches from Sydney, Nova...