The 21-year-old Misiewicz, who plays for FC Edmonton of the North American Soccer League, made a particularly stunning stop in the first half. El Salvador attacker Isidro Gutierrez was alone in front of the goal but Misiewicz got his hand on the shot. Gutierrez then sent the rebound wide left in the 20th minute.
"He made two great saves and he kept us in the game," said Canadian coach Tony Fonseca. "That's his job. He came up big and we appreciate that."
Jonathan Aguila had room in front of the net in the 90th minute when he went down in pain, missing the pass. He was placed on a stretcher and carried off the field.
El Salvador, which will play Cuba on Saturday, also had Andres Flores kick the ball over the crossbar in the 59th minute on a pass from Jaime Alas.
Canada's Sherif El-Masri had what could have been the best chance of the second half in the 79th minute, but he missed the target with the shot.
El Salvador outshot Canada 12-10 and had six corner kicks to Canada's five in front of 4,269 at LP Field.
Canada picked up just six fouls to El Salvador's 11, but Drew Beckie, Carl Haworth and Nana Attakora all drew yellow cards in the second half.
A player that accumulates two yellow cards in the tournament will receive a one-match suspension.
Canada's starting 11 featured nine players that have played for one of the nation's four professional teams: Montreal Impact, Toronto FC, Vancouver Whitecaps of Major League Soccer and Edmonton of the NASL.
Canada's next game is Saturday against the United States. The host U.S. shut out Cuba with an emphatic 6-0 win later Thursday.
Only two of the eight teams in the under-23 tournament go through to the London Olympics.
Canada has not qualified for the Olympics since the 1984 Los Angeles Games.
— With files from The Associated Press.