Shaman Ghost finished ahead of Danish Dynaformer in a battle of the 3-1 co-favourites.
The second-place finish was bitter-sweet for trainer Roger Attfield, who was looking for a record ninth Plate victory.
Shaman Ghost won the 1 1/4-mile race in an unofficial time of 2:03.45 at Woodbine Racetrack.
Conquest Boogaloo, at odds of 6-1, was third in the 13-horse field.
The second jewel of the Canadian Triple Crown is the $500,000 Prince of Wales Stakes on July 28 at Fort Erie Racetrack.