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Toronto, host to this weekend's Group of 20 summit, is preparing for an invasion of world leaders, police and protesters by shutting its doors.

The Toronto Blue Jays baseball team is leaving town, the Royal Alexandra Theatre is closing for the first time in more than a century and thousands of bankers and money managers such as David Cockfield are working from home.

"People coming to cover the G-20 are going to find Toronto just empty, with wind blowing through the downtown canyons, asking 'Where are all the people?' said Cockfield, a portfolio manager at MacNicol and Associates Asset Management.

Lost business from shuttered shops, offices, restaurants and tourist venues such as the Art Gallery of Ontario will likely offset any economic gains from packed hotels for the weekend summit in Canada's biggest city, Bank of Montreal deputy chief economist Doug Porter said.

The G-20 meeting may result in an average C$7500 ($10,200) in lost sales for each downtown restaurant during the two days, according to the Canadian Restaurant and Foodservices Association. That's a revenue drop of about C$23 million.

"Bottom line, restaurateurs are not liking it at all," association chief executive Garth Whyte said. "There'll be more losers than winners."

A 12-block section of Toronto's financial district is already surrounded by 3m-high chain-link fences and concrete barriers, part of the largest security operation ever in Canada with 20,000 police and security guards.

About 223,000 employees work in financial services in Toronto, the third-most of any city in North America, according to the Toronto Financial Services Alliance.

At least three dozen downtown branches of Canada's five largest lenders including Toronto-Dominion Bank and Canadian Imperial Bank of Commerce will close between June 24 and June 27 because of increased security and protests.

Bankers in the city's financial district on Bay Street are also being advised by their companies to ditch suits and ties for casual clothes, with at least 18 demonstrations planned by groups protesting everything from oil-sands development and poverty to boycotting Chilean wine and fruit.

"I'll probably wear a baseball cap and a pair of shorts," Sentry Select Capital money manager Mason Granger said. "I don't want to make it obvious I'm a Bay Street guy." Paul Hand, a managing director of equities at RBC Capital Markets, says he'll take June 25 off and come in later than normal to Royal Bank of Canada's gold-tinted office tower today.

The Brooks Brothers clothing store in the same building will be closed for three days.

"This whole G-20 thing has taken on a surreal feel," said Hand.

"It's become a backdrop of malaise."

Canada will spend as much as C$1.2 billion for the meetings to host world leaders, said Andrew MacDougall, a spokesman for Prime Minister Stephen Harper. By contrast, last year's G-20 summit in Pittsburgh cost US$18 million and London's tab was US$30 million, according to a report by the University of Toronto's G-8 and G-20 Research Groups.

The amounts in other countries may not be comparable, the group said.

The US Government issued an alert telling travellers to avoid downtown Toronto during the summit because of the potential for "violent and unpredictable" protests that started on June 21.

The shows won't go on at The Royal Alexandra Theatre and Princess of Wales, which are closed from June 21 to June 27.

"We'll be taking a sizeable loss," said producer David Mirvish.

"That week would have been enormous" because it was the last week for Mamma Mia. About 600 staff will lose their wages for the week, he said.

The Toronto Blue Jays shifted their three-game "home" series against the Phillies to Philadelphia to avoid the Rogers Centre stadium, beside the summit venue at the Metro Toronto Convention Centre.

Big Daddy's Crab Shack and Oyster Bar is among Toronto eateries planning to close this weekend.

"Nobody's going to be coming downtown," manager Trey Tran said.

Gabby's, a sports bar, is betting that full hotels will translate into booming business from police, journalists and summit delegates. The Royal Canadian Mounted Police are based at the Hyatt hotel across the road from Gabby's.

"The RCMP guys are going to be drinking here," Gabby's general manager Scott Wark said. "I don't expect any problems."