By Steve Keating

TORONTO (Reuters) - The Vancouver Canucks' dream season has quickly turned into a playoff nightmare that has left the Stanley Cup favorites on the brink of one of the greatest collapses ever in North American professional sport.

After running away with the Presidents' Trophy as the top team during the National Hockey League regular season and then racing to a 3-0 lead in their first-round series against the defending Stanley Cup champion Chicago Blackhawks, everything was going according to script for the Canucks.

But the plot has taken a dramatic turn over the past week as the Blackhawks have won three straight to level the series and set up a decisive Game Seven in Vancouver on Tuesday.

The mood in Vancouver on Monday was as dreary as the rainy West Coast weather as panic gripped the city a day after the team's 4-3 overtime loss in Chicago.

Even in the final week of a federal election campaign in Canada, the bigger discussion in Vancouver was not who might lead the country but who should start in net for the Canucks.

With Canadians eager to end an 18-year Stanley Cup drought, a sense of dread has suddenly swept across the hockey-mad nation as both Canadian teams left competing in the playoffs could be eliminated on the same night.

Many hockey fans in Quebec are feeling a similar angst as Vancouver supporters since the Montreal Canadiens, the only other Canadian team in the postseason, face a do-or-die Game Six versus Boston after squandering a 2-0 series lead.

Chicago appears to have Vancouver's number having bounced them from the playoffs in the last two seasons. But while the Blackhawks may have the momentum, history still sides with the faltering Canucks.

Only four times across North American professional sport have teams erased 3-0 deficits to win a best-of-seven playoff series; three-times in the NHL (1942 Toronto Maple Leafs, 1975 New York Islanders, 2010 Philadelphia Flyers) and once in Major League Baseball (2004 Boston Red Sox).

"We just have to feel like things are going to go our way," said Blackhawks captain Jonathan Toews. "We have to feel like it's meant to be.

"We have a great feeling in this locker room right now and that's what you get when you win three games in a row, stealing momentum from that team and fighting our way back."

Even among the small group of sporting flops, a Vancouver meltdown would stand out since the Canucks dominated play in the regular season, setting a franchise record for points, and scored more goals than any other team and allowing the fewest.

The team is stocked with talent, including Swedish twins Daniel and Henrik Sedin, who have claimed the Art Ross Trophy as top scorer in each of the last two seasons (Henrik in 2010 and Daniel 2011).

Guarding the net was Roberto Luongo, the goaltender who backstopped Canada to an Olympic gold medal last year and whose stellar work during the regular season earned him a nod as a finalist for the Vezina Trophy as the league's top goalie.

As the playoffs began, the Canucks were viewed as an NHL juggernaut taking on a shaky Blackhawks team that gained entry into the postseason by grabbing the eighth seed only after the Dallas Stars surrendered the final spot by losing to the Minnesota Wild in the last game on the schedule.

But the Sedins have been inconsistent, Daniel producing five goals while brother Henrik and team mate Ryan Kesler, who scored 41 times during the regular season, have none.

Vancouver's problems in net are far more dire.

His confidence shattered, a fragile Luongo started Game Six on the bench as a desperate coach Alain Vigneault turned to backup Cory Schneider.

"Sometimes you just got to go with your gut," said Vigneault explaining his decision. "Sometimes the book is over-rated and my gut told me it was the right thing to do."

(Editing by Frank Pingue)