Sinclair was chosen Sunday to lead the Canadian team into London's Olympic Stadium for the ceremony, which starts at 9 p.m. local time (4 p.m. ET).
"This is a huge honour and I wish I could have my teammates right here with me," said Sinclair. "We want the next generation of young girls to dream of being in the Olympics and getting a medal around their necks. If we can instill in them just the belief that this can happen, then we have done our jobs."
Sinclair captained the Canadian women's soccer team to a bronze medal — the first podium placing for Canada in a Summer Games traditional team sport since 1936.
The Burnaby, B.C., native was a popular choice after scoring an Olympic-record six goals in the women's tournament, including a hat trick in Canada's 4-3 extra-time loss to the United States in the semifinals.
Canada went on to defeat France 1-0 in the bronze-medal match on a dramatic goal by Diana Matheson in the 92nd minute.
Sinclair, 29, carried the Canadian flag at the opening ceremony of the Pan American Games last fall in Mexico.
Her 143 international goals tie her for the second-most of all time in women's soccer with active U.S. star Abby Wambach. Retired American Mia Hamm is the leader with 158 goals.
London set to 'party'
The Who, the surviving members of Queen and the Spice Girls were expected to headline a fun and frivolous closing ceremony, celebrating the remarkable crop of pop icons the host country has given the world for decades.
Artistic director Kim Gavin has promised "the best after-show party that's ever been," and as details of the lineup leaked in the British press days ahead of time, there was no reason to doubt him.
Eight minutes have been turned over to Brazil, host of the 2016 Games in Rio de Janeiro, which promises an explosion of samba, sequins and Latin cool. Following tradition, the mayor of London will hand the Olympic flag off to his Rio counterpart.
There will also be speeches by International Olympic Committee President Jacques Rogge and London organizing committee chief Sebastian Coe, and the extinguishing of the Olympic flame.
Canada short of medal goal
The United States edged China in both the gold medal and total medal standings. The U.S. won 104 total to China's 87, and 46 gold to China's 38, recapturing the gold-medal title it lost four years ago. Britain finished third in golds with 29.
Canada finish with 18 medals. That's the same number the country won in Beijing, but the 2008 team has the edge in gold medals (3-1) and silvers (9-5).
Canada's one gold medal is the fewest the country has won since the 1976 Montreal Olympics, where it was shut out.
The 2012 team fell just short of the Canadian Olympic Committee's goal of finishing in the top 12 in the overall medal standings, ending up 13th in total medals.
"We have so much to celebrate as we bring these wonderful London 2012 Olympic Games to a close," said Canadian team chef de mission Mark Tewksbury. "Every medal has a story and you can not underestimate the power and the impact that each and every one has had. We are so proud to honour not only our medallists, but all members of the Canadian Olympic Team."