In a race filled with caution flags, the 22-year-old Englishman won in his sixth F1 start and now has six consecutive top-three finishes.

The only one to give the Mercedes McLaren driver any competition during the 70-lap race on Circuit Gilles Villeneuve's 2.71-mile road course was BMW Sauber's Nick Heidfeld. He chased Hamilton all day without catching him. Hamilton beat Heidfeld to the finish by 4.3 seconds.

Two-time and reigning F1 champion Fernando Alonso, who started alongside his pole-winning McLaren teammate on the front row, made a mistake on the start when he drove off the course in Turn 1 .

That was just the beginning of a very bad day for Alonso, who was hit with a penalty for pitting too soon during one of the full-course cautions and made two other off-course excursions before being passed two laps from the finish by Super Aguri'a Takuma Sato and finishing seventh.

Robert Kubica, a 22-year-old driver from Poland, was involved in a frightening crash just before the halfway point. He escaped serious injury but was taken to a hospital for further examination after being removed from his battered car by medical personnel. Team officials said Kubica apparently sustained only a foot injury.

Considered one of the rising stars of the international series, Kubica was racing with the Toyota of Jarno Trulli and the Ferrari of Felipe Massa when he suddenly veered off course into the grass as they drove toward the hairpin turn.

Kubica's BMW Sauber slammed into the inside concrete wall, then somersaulted across the track in a shower of debris, hit the outside wall and came to rest with what was left of his car on its side.

The Ferraris of Felipe Massa and Kimi Raikkonen were expected to pose a threat for the McLarens, but both had their own problems.

Massa was running fourth when he was disqualified, along with Renault's Giancarlo Fisichella, who was eighth at the time. F1 officials said they both ran a red light at the end of pit road during a caution period.