Sly grew up in Ottawa, joined local boys and adult choirs and studied music at McGill University. In 2011 he was one of the winners of the Metropolitan Opera National Council Auditions, during which time he was taught by Cynthia Hoffmann and receipient of the Choquette-Symcox Award conferred by JM Canada Foundation and Jeunesses Musicales Canada.The following year, 2012, he won the Grand Prize of the Montreal International Musical Competition.