Marchment also had an assist, and Yaroslav Askarov made 23 saves for the Sharks (7-6-1), who snapped a two-game losing streak.
"The message was pretty clear: just go play, loosen up a little bit. I think we were trying to choke out a goal and choke out a win," San Jose coach Ryan Warsofsky said. "We were gripping it really tight. You could see it, you could feel it."
Drew O'Connor and Liam Ohgren scored for the Canucks (3-11-1), who are 1-10-1 in their past 12 games. Merilainen made 21 saves.
"It continues to be the biggest problem with our group is the lack of details in key moments," Vancouver coach Manny Malhotra said. "Face-off details once again plague us. The PK didn't get the shot block we needed."
O'Connor put the Canucks up 1-0 at 13:21 of the first period. Forward Elias Pettersson kept the puck in at the blue line, and his wrist shot kicked off Askarov's right pad back in front, and O'Connor tapped it in while he was crashing the net.
"I think our third period wasn't good enough, obviously," O'Connor said. "I don't think we did the same thing we did in the first two periods. Just didn't manage the puck well enough in key areas."
Ohgren scored for the second straight game to push the lead to 2-0 at 18:56 of the second period. He took the puck in from the right boards, and his wrist shot from the slot beat Askarov over the blocker.