The Polish star was defeated 6-2, 6-7(4), 6-4 by American world number three Pegula on Saturday.
Świątek last month defeated Germany's Laura Siegemund 6-0, 6-1 in the final of the Poland Open tournament in Warsaw, claiming her 15th career singles title.
The 22-year-old, coached by countryman Tomasz Wiktorowski, has topped the world rankings in women's tennis since April 4, 2022.
The Canadian Open is a combined women's and men's hard-court tournament held annually in Montreal and Toronto. This year's event runs until Sunday.
(ał)
Source: PAP