 Cantoni was born in Lenno on 1 September 1950 and had moved with his family to the nearby village, Tremezzo, at the age of eight.In 1970, after studies at the Pontificio Collegio Gallio founded by the Somaschi Fathers, he entered the diocesan seminary in order to receive specific theological preparation.In 1975, Cantoni was ordained a priest in the province of Como by bishop Teresio Ferraroni.