Lynn Horne, Hynes' manager, said Hynes will be starting treatments of radiation and chemotherapy in the middle of August.
Horne said all of Hynes' upcoming performances have been canceled, with the exception of one show with the Wonderful Grand Band at Mile One Centre on Aug. 11.
Horne said Hynes is taking strength from the support of his family, friends and fans.
"He writes tender songs but he's a tough man," said Horne. "He's an eternal optimist and he's a man of strong faith and he's loved by many and their prayers and good thoughts are most welcome."
Hynes, whose songs, such as Sonny's Dream, have been covered by dozens of artists worldwide, announced he was unwell at a performance on July 15.
Hynes is a six-time East Coast Music Award winner and Genie award winner.