The signing is pending his international transfer.
Montaño, 20, played two games with the Sounders' first team in 2011 and eight games, including five starts, with the reserve team, tallying one goal and two assists in 465 minutes.
In 2010, he played 12 games with the Sounders, in all competitions, including six as starter, tallying two assists in 535 minutes of play. The previous season, he scored 13 goals in 19 games with Club Atlético Quilmes, in Argentina. In 2008, he scored 18 goals in 24 matches with the reserve team of Columbian club Envigado FC.
Internationally, Montaño played one game with Columbia's Under-20 national team, against Ecuador, on April 22, 2010.
"He is a fast and technical player, who can play as forward or wide out," said the Impact sporting director Nick De Santis. "He has played at this highest level in North America and will bring more depth to our team. He is excited to come to Montreal. We will have the chance to see him."