Buchanan charged into the box on a corner kick and her header bounced into the goal. But all eyes were on her teammate Christine Sinclair, who is four goals away from becoming the sport's all-time international top scorer.
Sinclair sits at 181 goals, trailing only former U.S. forward Abby Wambach, who had 184 goals in international competition to set the record among men and women.
The Canadian captain's free kick was blocked and cleared away in the 51st minute, and she had another good chance in the closing minutes. She had scored in the opening game of each of her previous four World Cup appearances.
Cameroon was a surprise at the 2015 World Cup, advancing out of the group stage before falling to China in the round of 16.