Larin opened the scoring in the fourth minute when he headed home from Sam Adekugbe's looping cross before David added another nine minutes later, pouncing on a loose ball after goalkeeper Saad Al Sheeb had failed to deal with a cross.
Qatar employed a deep defensive line and offered little in attack, with Abdulaziz Hatem's powerful shot from distance, which was tipped over by Milan Borjan, their best effort of the opening half.
Canada manager John Herdman made wholesale changes after the break, including taking off Bayern Munich's Alphonso Davies, in search of a third but they were thwarted by Qatar who could have claimed a late consolation through Karim Boudiaf.
Canada, who last appeared at the World Cup in 1986, play Uruguay in a friendly on Tuesday and Qatar next face Chile.
