First few paragraphs from the article:

John Candy met talent agent Catherine McCartney by accident. Striking up an awkward conversation after nearly knocking her over in line at the Eaton’s cafeteria, he discovered that her talent office just happened to be across the street, next to Fran’s Restaurant where he sometimes dined. McCartney later saw him at Fran’s and invited him up to her office, where he shyly confessed to her that he had been taking acting classes with an eye toward becoming a professional actor. Charmed by Candy’s baby face and disarming wit, McCartney was eager to help him get a foot in the door. In 1970, she happened to be casting for a television commercial in which a high school football player would expound on the virtues of Colgate toothpaste. She knew just who to send out on the audition.

Candy had played this character in real life, and after passing the audition, he found himself walking across a studio floor in full football padding to a locker room set where he joined Canadian-born icon of American television Art Linkletter, whom Candy recognized from his 1950s television program People Are Funny. “My one big line was ‘Oh sure, Casanova!’” Candy later told David Letterman on his Late Night talk show. “[We did] about a hundred takes of that.”

Candy immediately felt at home on set and discovered an instant and easy rapport with the film crew, breaking up a long day with well-placed laughs between takes. The Colgate spot gave him confidence to ask McCartney to send him out for more commercials, and he booked a few. One was for Molson Golden Ale, and Candy was thrilled to see it running constantly during the CBC’s Hockey Night in Canada broadcasts, where all of his old Neil McNeil High School pals were sure to see it.