Justin Trudeau has summoned his new cabinet, one by one, to a private office on Parliament Hill where they have been vetted by security officials and sworn to secrecy, CTV News has learned.

Sources say the future ministers were told to stay quiet about their new jobs or risk losing them before the swearing-in on Wednesday.

Trudeau is expected to do away with the traditional limousines to the Rideau Hall ceremony, and many are speculating about who will be stepping off the bus behind him.

With an expected cabinet of 28 ministers, Trudeau would not have had trouble keeping his promise for gender parity. There were 50 women elected to his 184-member caucus in October.

But aside from gender, what else did the prime minister-designate weigh while choosing the team?

Eddie Goldenberg, a former senior advisor to Jean Chretien, told CTV Power Play that a few factors would likely have been taken into consideration.

Among them is regional representation. “There’s a convention that you need provincial representation and that’s important,” Goldenberg said. “We’re in a federation.”

Another factor is ethnic diversity. “In an era of globalization … ministers born in other places are fantastic ambassadors for Canada around the world trade-wise,” Goldenberg said. “And it’s also useful just in terms of the integration of communities into the Canadian fabric.”

A mix of veterans and rookies is also a good idea, according to Goldenberg. “You need some people who have been in the cabinet room before, because they can help mentor people who were not in there. And you need a lot of fresh faces with new ideas.”

Tim Murphy, who helped Paul Martin form his cabinet in 2004, agreed that “it’s entirely possible you could see relatively fresh faces in senior portfolios.”

While Goldenberg said occupations outside politics may have been taken into account, political strategist Rick Anderson said that wouldn’t have been wise.

“It’s generally a good idea not to have a teacher in charge of the education portfolio, not to have a health professional in charge of the health portfolio, not to have a banker in charge of the finance department, a military person in charge of defence,” Anderson said. “There’s a long history of (such ministers) not succeeding because maybe their perspective is too narrow.”

After Trudeau’s promises to improve relations between Canada and first nations, many will be watching to see how many Aboriginal Canadians have made it into the inner circle, and whether an indigenous person was chosen as Minister of Aboriginal Affairs and Northern Development.

There are several such options. A record 10 MPs with indigenous backgrounds were elected on Oct. 19, including Liberals Yvonne Jones, Vance Badawey, Don Rusnak, Dan Vandal, Robert Falcon-Ouellette, Jody Wilson-Raybould, Michael McLeod and Hunter Tootoo.

Assembly of First Nations National Chief Perry Bellegarde said he believes having more Aboriginal people in cabinet would be good for Canada, but did not say whether he thinks the Aboriginal Affairs minister ought to be indigenous.

“No matter who is appointed, that they have a respectful relationship with First Nations leadership is the most important thing,” Bellegarde said. “The prime minister has a very tough choice.”

With a report from CTV’s Ottawa Deputy Bureau Chief Laurie Graham

Swearing-in ceremony at Rideau Hall: