The US men's team beat Italy 46-26 to secure a sixth straight title, while the women's side missed out on a fourth straight after losing 27-20 to Canada.
"Gold is the only standard," said US men's quarterback Nico Casares, who threw two touchdown passes. "That's our motto. That's what we play by, that's what we live by."
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The US women's side started strongly but it was tied 14-14 at the break after Caroline Moquin-Joubert caught Canada quarterback Sara Parker's pass at the end of the first half.
Parker then set up Frederique Morneau at the start of the second half as Canada took control.
The US had a fourth down, yards from the line, with three seconds left, but could not make the final play count. It was Canada's third title and first since beating the US in the 2014 final.
The top two men's and women's teams outside of the US men's and women's teams - because they already qualified as hosts - also earned spots at the 2028 Olympic Games.
Sunday's two other finalists - the Italian men and Canadian women - earned their place by reaching the final against the US teams, meaning that the bronze-medal games decided who joined them.
Mexico women cried with joy after a 20-19 win over Great Britain - who rallied from 20-6 down - for the women's bronze and an Olympic spot.
But Mexico's men lost 34-26 in overtime to Canada, who claimed an Olympic spot.
