The match was played at Lockhart Stadium, Florida - behind closed doors, which meant neither team got much support from the stands.
Ouimette entered the game in stoppage time, essentially having enough time to help defend a corner (around the 1:52:00 mark in the full match video below) and help Canada hang to the clean sheet and the win.
The goal came from Marcus Haber in the 10th minute: a header off a corner.
Canadá venció ayer a Guatemala con este gol de Marcus Haber pic.twitter.com/uDqfubicPy— Fútbol Puerto Rico (@FutbolPR_) March 28, 2015
Canada's immediate objective is to find a settled squad and effective playing style for this summer's CONCACAF World Cup qualifying matches (Canada will face Dominica or the British Virgin Islands in June) and Gold Cup.
To that end, recent results have been encouraging. Canada has two wins and a draw from its last three games against CONCACAF opposition: it beat Jamaica in Toronto in September, drew with Panama in Panama in November, and has now beaten Guatemala in Florida.
The team and Ouimette will hope to keep the run going against Puerto Rico in Bayamon on March 30.