Dan Boyle, Joe Thornton and Logan Couture also scored to keep the Sharks unbeaten in five games. Antti Niemi made 24 saves for the shutout.
Eddie Lack stopped 28 shots for the Canucks, who lost their second straight on the road.
Hertl opened the scoring at 10:37 of the first period, redirecting a shot by Scott Hannan. Boyle's goal came two minutes later.
Thornton scored at 11:21 of the second period directly after Couture won a faceoff during a power play. Couture added a power-play goal with a minute left in the period.
Hertl, who has a team-leading three goals in the preseason, scored his second goal at 2:25 of the third.