"The site can't keep up with the demand," said Tara Wood, manager of public relations for World Wildlife Fund Canada.
Canada has maintained a strong position in official worldwide sign-ups at the site, despite slipping just behind the United States. "I'm holding out hope that Canadians will pull through and take the lead again," said Wood.
Just recently, Canada was in first place, but now trails the U.S. about 2,000 with close to 55,000 people who have officially committed, via earthhour.org, to turning off their lights from 8 to 9 p.m. Saturday.
On a per capita basis, though, Australia leads at about one in 420 people signed up; Canada has one in 606 and the U.S. one in 5,347.
Enthusiasm in the GTA has been phenomenal, Wood said, with 15,000 signed up by March 19. The rush has made it impossible for organizers to gather the latest city-by-city numbers.
"I think there's a good possibility we could be the world leader. I think it is Sydney that will be our biggest competition," she said. "They've been through this drill once before."
When Earth Hour began in Sydney last year, an estimated 2 million people took part, of which only 50,000 officially signed up. Most participants won't sign up online this time, either. The real impact will be measured by the amount of energy conserved Saturday night.
Still, Kasia Wallis, online manager with WWF in Australia where the site is maintained said by telephone that officials were overwhelmed by worldwide interest. Traffic to the website has been doubling every second day.
"We never dreamed, we never anticipated, there would be such demand," said Wallis. "But that's a good thing a great thing. We're very excited."
Toronto's plans for March 29 include a free concert at Nathan Phillips Square headlined by Nelly Furtado, starting at 6:45 p.m.
Tents used for Fashion Week were coming down to be replaced by a stage. Several tests have been run this week to ensure the City Hall lights go off at 8 p.m.
With many businesses on board, it is expected the city's skyline will disappear after Furtado delivers an acoustic concert including her hit song "Turn Off the Light."
Canada's desire to reduce its environmental impact is evident in the number of cities more than 150 that have indicated they'll reduce power use that night, Wood said.
Toronto's Michel Fortier, 25, said he knew as soon as he heard of it a couple of months ago that he would participate. But turning off the lights is just the beginning, he said. "I've been really excited about this. It is a great cause and I'm going to be turning off everything that day."
Having studied construction engineering, Fortier dreams of building solar panels and wind turbines for industrial buildings. Earth Hour has made him more conscious of things he can do like recycle more and reduce power use every day. "It is so simple and it makes a difference," said Fortier.
Facebook now has more than 500 Earth Hour-related groups and, according to an Angus Reid online poll conducted recently, 70 per cent of Canadians plan to take part.