Cantancio was just 18 years old when he won a bronze medal in the bantamweight division at the 1981 Southeast Asian Games held in Manila. The Bago native took part at the 1982 AIBA World Amateur Championships and was eliminated in the Round of 16. He also participated at the 1982 Asian Games in New Delhi as a featherweight and was knocked out by North Korean Jo Rion-sik in the quarterfinals.