Open this photo in gallery: Brian McKenna, right, and future Prime Minister Justin Trudeau portraying his fifth cousin, Major Talbot Papineau, in The Great War.Arnie Gelbert On Remembrance Day, 1987, documentary filmmaker Brian McKenna brought his young family to the cenotaph in Westmount, Que. The memorial is a tribute to the sacrifice of local citizens who died on the battlefield during the First World War. “We were all decked out in scarlet poppies watching old soldiers in blue berets and clanking medals, remembering and praying,” Mr. McKenna said in 1992. After the ceremony, one of his daughters, Robin, ran her...