Armstrong, 31, missed out on a medal in Beijing in 2008 by one centimetre despite breaking the national record.
Canada has already won two silver and five bronze so far at the Games but is still yearning for the gold.
Armstrong has a personal best of 22.21 and will go up against America’s leading trio Christian Cantwell, Reese Hoffa and Ryan Whiting among others for gold in London, Reuters reported.
Alex Gardiner, Athletics Canada head coach, expressed his confidence in Armstrong.
He said: “He’s recorded a couple of workouts that have been better than any he’s had in his life. When I heard from him three days ago that he had a personal best in one of his training sessions, I know that he’s ready. And he’s honest as the day is long.”
The six-foot-four 345 pound Armstrong is just one of eight members of Canada’s 45-strong Olympics squad to have experience of a previous Games.