By Steve Keating

TORONTO (Reuters) - Henry Burris threw three touchdowns, including one in overtime, and ran in two others as the Ottawa Redblacks stunned the Calgary Stampeders 39-33 to win the 104th Grey Cup in one of the biggest upsets in Canadian Football League history on Sunday.

Burris was named the game's Most Valuable Player after completing 35-of-46 passes, none bigger than the 11-yard strike to Ernest Jackson in overtime that gave Ottawa their first Grey Cup for 40 years, when the team were known as the Rough Riders.

The 41-year-old Burris, who also connected on touchdown passes to Brad Sinopoli and Patrick Lavoie and threw for a total of 461 yards, became the oldest quarterback to lead his team to a Grey Cup triumph.

The Redblacks' victory over the heavily favored Stampeders also erased the disappointment of losing to the Edmonton Eskimos in last year's title showdown.

"It was almost a situation where I wasn't able to play today, my knee locked up on me before the game but I wouldn't accept that," said Burris, who guided the Stampeders to the CFL championship in 2008.

"For all those haters out there, all those organizations who haven't won a Grey Cup for decades, here we are.

"Right now all I want to do is enjoy the party."

The Redblacks ended the season with an 8-9-1 record and were not expected to represent much of a problem for a Calgary juggernaut that had ripped through the schedule (15-2-1) behind the league's outstanding quarterback Bo Levi Mitchell.

But Ottawa fans, who had seen both the Rough Riders and Renegades fold since they last celebrated a Grey Cup in 1976, were ready to party early as the Redblacks rolled to 20-7 halftime lead.

When Burris found Sinopoli with a nine-yard touchdown pass to open the second half, some in the sellout crowd at BMO Field were already preparing to make a swift exit and avoid the rush.

The Stampeders, however, would not go down without a fight, turning the rout into a nail-biter by scoring 10 points on a DaVaris Daniels touchdown run and Rene Paredes field goal in the final two minutes to send the game into overtime.

Even the decisive touchdown did not come without a fright as Jackson wildly juggled the ball before finally gaining control as he crossed into the end zone to cement the victory.

"It hurts, we made the largest comeback in Grey Cup history we just didn't finish it," said Mitchell, who tossed two touchdowns but was intercepted three times. "We had the opportunity we put ourselves in perfect position to finish it."

(Editing by Peter Rutherford/John O'Brien)