The Canadians are the reigning gold medallists after winning at the Tokyo Games two years ago.
They went into the match on Tuesday night in Toronto with the advantage after defeating Jamaica 2-0 in the first leg last week in Kingston.
The United States had already secured the first of CONCACAF's two spots in the field for the Olympics.
Drew Spence gave Jamaica the lead from a free kick that sailed over the wall and tucked into the corner, out of reach of home goalkeeper Kailen Sheridan in the 33rd minute.
After a pair of shots hit the crossbar, Canada broke through in the 39th with a goal by Lacasse that put the team up 3-1 on aggregate.
Huitema came into the game as a second-half substitute and scored in the 50th before a packed house of 29,212 at BMO Field.
Canada have won a gold and two bronze medals from women's soccer at the last three Summer Games but their coach Bev Priestman conceded there is plenty of work ahead if her squad are to return to the podium in the French capital.
"It's exciting but I am not getting carried away by any means because we've got some real hard work to do," Priestman said.
"To go and get on the podium again, and you've just seen at the World Cup, it is going to be harder than it has ever been."
Canada were coming off a disappointing finish at the Women's World Cup this summer. They didn't advance out of the group stage after losing 3-0 to co-hosts Australia and drawing 0-0 with Nigeria. Jamaica fell to Colombia in the round of 16 in their best-ever World Cup performance.
"I've thought about this game from the minute that World Cup ended so everybody has put a real shift in to do whatever we could to turn this around," Priestman added.
"This team is better when they're going after something and ultimately we are going after putting the wrong right of that World Cup."
With Reuters.
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