Philadelphia Flyers rookie goaltender Carter Hart stopped all 12 shots he faced for Canada’s first win of the tournament.
The Canadians opened the international event with a 3-1 loss to Finland on Friday.
Mathieu Joseph, Dylan Strome, Dante Fabbro and Sean Couturier rounded out the attack for Canada.
Ben Bowns turned aside 40-of-48 shots he faced in 50 minutes of work in net for Britain. Jackson Whistle made eight saves the rest of the way.
Joseph opened scoring for Canada 2:42 into the game. Defenceman Darnell Nurse’s point shot was blocked by a British defender, with Adam Henrique gathering the loose puck to put a backhanded shot on Bowns. That rebounded to Joseph who snapped the puck into the net.
Jared McCann’s strong individual effort led to Canada’s second goal as he carried the puck through all three zones and then fed Mantha for the easy tap-in goal and a 2-0 lead.
Mantha has his hand in on Canada’s third goal, breaking down the side of Britain’s defensive zone and feeding a streaking Turris who deked out Bowns to put the puck in the back of the net for a 3-0 lead 2:35 into the second.
Canada struck again at the 7:05 mark of the second period while on a power play. Jonathan Marchessault wired a wrist shot at Bowns, who got a piece of the puck. As it dribbled through the crease Strome took a couple of backhanded whacks at it before knocking it into the net.
With just 23 seconds left to play in the second period Fabbro stepped into a booming slapshot, drilling the puck past Bowns for a 5-0 lead.
Turris put away his second goal of the game just 57 seconds into the third period, with Couturier and Mantha finding the back of the net within the next 10 minutes for the final score.