When she was Quebec's minister of immigration, Yolande James barred a Muslim woman from attending French-language classes because she refused to remove her niqab during an exam.

"There is no ambiguity on this question: If you want to [attend] our classes, if you want to integrate in Quebec society, here our values are that we want to see your face," Ms. James said in 2010.

Ms. James now says her views have since evolved. Running to succeed Stéphane Dion as the MP for the Montreal riding of St-Laurent, Ms. James said she fully agrees with Prime Minister Justin Trudeau's more open approach to religious minorities.

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"I've obviously had a lot of time to think about that and to talk to members of the community," said Ms. James, who is the daughter of immigrants from the Caribbean. "I would do it differently, I would see the situation differently."

The 39-year-old has a number of key allies in the Liberal hierarchy, and her high profile in provincial politics would lend the Prime Minister a valuable voice in Quebec – a province that is looking for a stronger role around the federal cabinet table.

A by-election for the riding has been called for April 3. Given St-Laurent is a traditional Liberal stronghold, the party's nomination in the multiethnic riding is expected to be bitterly contested, which explains why Ms. James now has to account for her past decisions.

"I have a deep unease with politicians who change their discourse on issues of fundamental rights," said Marwah Rizqy, a professor of fiscal law who is also running for the nomination.

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Ms. Rizqy, who is the daughter of Moroccan immigrants, added: "Politicians have an obligation to protect all cultural communities, and that cannot be done on the basis of public-opinion polls."

The other main candidate in the race, Pakistani-born businessman and long-time municipal politician Alan DeSousa, also took a shot at Ms. James.

"Each candidate, including Ms. James, has a track record," he said. "I invite all of the voters to look at our track records closely, at our positions, at our achievements, at what we have done."

Still, there are concerns among rival camps that the race is being organized in such a way as to favour Ms. James.

They point out that three of Ms. James's ministerial aides from her days in the National Assembly in Quebec City now have senior roles in the Trudeau government. While she has yet to speak to Mr. Trudeau, sources said that Ms. James has been in touch in recent weeks with senior officials in the Prime Minister's Office.

In addition, she brings ministerial experience to the table and benefits from a high level of name recognition in Quebec, where she was a political analyst on a top-rated news show for the past three years. In a province where the federal government struggles to generate media coverage, a number of Liberal officials feel she would become a key player in the government.

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Now mayor of the borough of St-Laurent, Mr. DeSousa is banking on his own local organization in the nomination battle, having easily won a series of municipal elections on the exact same territory as the federal riding.

"I know my community backwards, forwards, inside out. I could be sleepwalking and I would know geographically where I am, but also what are the subtle needs of the community," Mr. DeSousa said.

St-Laurent is at the heart of debates in Quebec over the treatment of minorities. The woman who was denied access to a French class in 2010, Naema Ahmed, was attending a college in the riding. She is now living in the Toronto area with her family "The way [Ms. James] treated my wife was really bad," Ms. Ahmed's husband, Waleed Aboziad, said in an interview. "We were not welcomed, so we left."

Ms. James explained her goal at the time was to favour the integration of immigrants in Quebec. She said ensuing events – including the PQ's proposed charter of values – proved that restricting the use of religious symbols was the wrong approach.

"The intention was to favour integration, but … everything that has happened has been the exact opposition. There has been a population that has been stigmatized," she said. "This leads me to believe that it was not the right approach."

In the government of Jean Charest, Ms. James was the minister of immigration from 2007 to 2010, and the minister of family from 2010 to 2012. She quit the National Assembly in 2014 to take care of her newborn son, but now feels ready to return to politics, starting with the nomination race.

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"I expect it to be tough, but I'm pretty tough, too," she said.

Mr. DeSousa said he simply wants the process to be fair.

"I wasn't born yesterday, I'm quite aware of how party politics work," he said. "But I believe the Prime Minister when he says he wants people who represent the grassroots."