Prime Minister Justin Trudeau joined a unanimous vote in the House of Commons on Tuesday on an opposition motion that urges his government to "respect the custom of regional representation" when it fills a current opening on the Supreme Court.

The 270-0 result appears to repudiate Mr. Trudeau's approach to his first top-court appointment. Since its creation in 1875, the Supreme Court has always had a judge from Atlantic Canada, and Justice Thomas Cromwell of Nova Scotia retired on Sept. 1, creating the vacancy. Mr. Trudeau opened the search for his successor to the whole country.

The appointment has been more fraught than most, a behind-the-scenes contest between regional diversity and the government's expressed desire to appoint more women, visible minorities and aboriginal people to the bench.

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A spokeswoman for Justice Minister Jody Wilson-Raybould said the vote means only that the government has committed to include candidates from Atlantic Canada on the shortlist for the position.

"The Minister is confident that excellent jurists from Atlantic Canada applied and will be on the short-list," Valérie Gervais said in an e-mailed statement.

And an aboriginal legal star who might have provided a political justification for breaking with convention told The Globe and Mail it is important to respect Atlantic Canada's wish for regional representation. She declined to say whether she was contacted during the appointment process.

"I've learned a very important lesson in my career: Although I've had to break down barriers, I never go where I'm not invited," Mary Ellen Turpel-Lafond told The Globe and Mail the evening before the surprise Commons vote on the motion sponsored by Conservative MP Rob Nicholson.

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There had been talk in senior legal and judicial circles as far off as Newfoundland and Labrador that Ms. Turpel-Lafond, currently in British Columbia, had the inside track to become Canada's first aboriginal Supreme Court justice this fall.

The appointment is a chance for Mr. Trudeau to follow in his late father's footsteps. Prime minister Pierre Trudeau named the first Jewish judge, Bora Laskin, to the Supreme Court in 1970. (He broke another tradition three years later by naming Mr. Laskin chief justice, bypassing the court's senior judge, Ronald Martland.) But candidates to be the first aboriginal or visible minority Supreme Court judge are scarce in Atlantic Canada – one reason, Liberal insiders say, Mr. Trudeau chose not to limit the search to that region.

The 52-year-old Ms. Turpel-Lafond has a doctorate in law from Harvard University. She is bilingual, which Mr. Trudeau has made clear is a requirement for Supreme Court appointees. No other aboriginal candidate has such a wide-ranging a background in government, the judiciary, academia and aboriginal affairs. Ms. Turpel-Lafond is B.C.'s Representative for Children and Youth, on leave for the past decade from her job as a judge on the Saskatchewan Provincial Court.

But Atlantic Canada is not yet prepared to accept that other kinds of diversity are more important than regional diversity on the court, she said.

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The four East-Coast provinces are "a very significant part of the country that tends to be underrepresented, and I wouldn't want in any way to push forward through any of those important customs."

She added: "The local bar and bench and others need to support the person. I haven't experienced that support. No one has reached out to me to give me that support. So I'm an outlier. It would be very unwise to go into a position where you are not supported."

Politically, the Liberals owe a great deal to Atlantic Canada; they won all 32 seats in the four Atlantic provinces in the election last fall. And they have rewarded the region by choosing the Speakers of the Commons and the Senate from there.

Provincial politicians from the East Coast and the Canadian Bar Association have urged Mr. Trudeau to preserve the seat on the country's highest court for Atlantic Canada. And the Atlantic Provinces Trial Lawyers Association filed a legal challenge even before a new judge has been appointed.

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Its spokesman, Raymond Wagner of Halifax, called Ms. Turpel-Lafond's attitude "admirable" and said the most prudent thing for Mr. Trudeau to do would be to appoint her when Chief Justice Beverley McLachlin reaches the retirement age of 75 in two years.

Of the Commons vote, he said in an interview, "I think it means [Mr. Trudeau] should be looking at making an Atlantic Canadian appointment, because that's the will of the people."

Mr. Nicholson said he believes the government listened to criticism – including from backbenchers in its own caucus.

"I'm trusting that they'll do the right thing and appoint somebody from Atlantic Canada," he said.

With a report from Laura Stone

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