Ondrej Kase scored his 10th of the season at 14:03 on a redirection of Bunting's feed to make it 3-1.
Grubauer has allowed three goals in three of his past four starts. The Kraken were outshot 11-6 in the first period.
''At that point, you're at a point where you give up another one and now you're in a real deep hole, so (I) really just wanted to change the momentum and try to push the other way,'' Hakstol said of the goalie change.
Marner made it 4-1 at 9:15 of the second period with a shot from the right circle. It was his 400th NHL point.
"Obviously, it's a pretty cool achievement," Marner said. "I've obviously got to thank my parents, a lot of people around me; without them, this isn't possible."
David Kampf scored shorthanded at 3:37 of the third period off a backhand pass from Marner to make it 5-1.
McCann scored a power-play goal at 6:52 when his shot squeaked between Campbell's skates and trickled over the goal line to make it 5-2. It's the first time McCann has scored 20 goals in an NHL season.
"It's obviously very special," McCann said. "It's something I've worked very hard for, especially in the summertime. It's a dream come true to make it to the NHL, so I'm just trying to take advantage of it."
Jake Muzzin scored at 18:19 for the 6-2 final.
NOTES:Matthews extended his point streak to eight games (seven goals, nine assists). … Bunting is the sixth Maple Leafs rookie in the past 10 seasons to score at least 15 goals, joining Matthews, Marner, Nylander, Andreas Johnsson and Connor Brown. … Marner (120 goals, 280 assists) is the second player from the 2015 NHL Draft to score 400 points, joining Edmonton Oilers center Connor McDavid. … Jarnkrok has two goals and two assists during a three-game point streak.