Larin ran past the defence for a loose ball and juked a sliding El Salvador goalkeeper Derby Carrilo in the 35th minute, but his shot on an open net went high and wide.
"The miss by Larin is part of the game, it happens," said Canada's coach Benito Floro through a translator.
Tosaint Ricketts had another chance for Canada in the 43rd minute — beating two defenders during a breakaway — but his shot from 15 yards out went high.
"I think nil-nil was a fair result, if not us edging it," said David Edgar, who was serving as captain for the first time in his international career.
"Our strikers held their heads up high. They made some chances and they will get back in those positions again. We just have to keep working as a team and the goals will come."
Right before halftime, El Salvador's Richard Menjivar beat three defenders with nifty footwork to get next to the near post. But his centring pass was cleared away. Moments later, Canadian goalkeeper Kiriakos Stamatopoulos misplayed a punch-out, but he recovered to block Irvin Herrera's close-range shot.
Stamatopoulos was tested often for Canada and made six saves. He started in place of No. 1 goalkeeper Milan Borjan, who is missing the tournament because of his Bulgarian club commitments.
The Canadians are ranked 109th in the world and 13th among CONCACAF countries. El Salvador is ranked 89th internationally.
Canada continues Gold Cup play on Saturday in Houston against Jamaica.
"The analysis of all four teams in Group B after one matches is that all teams are very equal," said Floro. "We are playing in the strongest group at the Gold Cup. Both Canada and El Salvador will pose challenges to Jamaica and Costa Rica."
The draw improves Canada's unbeaten streak to six matches.
Larin and Tesho Akindele were making their Gold Cup debuts for the Canadians.
Canada won the Gold Cup in 2000.
With files from The Associated Press