Liberal efforts to court rich pension funds and foreign investors to boost infrastructure spending are under attack from the left and the right, which accuse Prime Minister Justin Trudeau of selling out the public interest.

Interim Conservative leader Rona Ambrose criticized Mr. Trudeau on Wednesday during a public speech to her party's caucus, claiming sarcastically that the Prime Minister should be able to work well with Donald Trump because of the U.S. president-elect's vast wealth.

"Prime Minister Trudeau loves hanging out with billionaires. This could work out," she said. "Our Prime Minister sure likes spending time with them. He spends time with them in Davos, at a billionaire retreat in Sun Valley, with Chinese billionaires at Meech Lake and, early this week, with hedge fund managers and billionaires at the Ritz Carleton."

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Ms. Ambrose was referring to Monday's closed-door meetings in Toronto, at which Mr. Trudeau and senior cabinet ministers met with Canadian-based institutional investors at the Ritz Carleton and then went in the afternoon to a meeting with foreign investors organized by BlackRock Inc., the world's largest asset manager, at the Shangri-La Hotel.

The Liberals used the meetings to promote their proposed new $35-billion Canada Infrastructure Bank, which would aim to develop a priority list of projects worth at least $100-million each that combined public money and private investment dollars.

Ms. Ambrose said the "so-called infrastructure bank" would go against the interests of the Canadian middle class, which the Liberals claim to be helping.

"Let me just decode this for you. It's a plan to take loans for bridges, hospitals and schools from foreign billionaires. Billionaires who, let's make it clear, they're not doing this out of the best interest of Canadians. They're going to be looking for a return, and that means jobs will be a cost that's kept to a minimum, and taxpayer dollars will come second to their profits whenever there is a project that goes over budget. So that means that decisions about tolls and user fees will be made in boardrooms in Beijing and Dubai. Not here."

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The NDP is continuing its opposition to public-private partnerships, and public-sector unions are bolstering their attacks this week, releasing opinion pieces and union-commissioned polls to argue that the public does not support such arrangements.

The Conservatives, however, have been strong advocates for more private investment in infrastructure. The Conservative government created a federal Crown corporation called PPP Canada in 2009 that is similar to the proposed infrastructure bank, but has a much smaller budget. The Conservatives also required municipalities to test all infrastructure-spending projects for their potential to be delivered through a public-private partnership. The Liberal government removed that test, and Infrastructure Minister Amarjeet Sohi told The Globe and Mail this week no decision has been made on the future of PPP Canada.

Conservative spokesman Jake Enwright said the party remains philosophically supportive of public-private partnerships, but is concerned about the lack of detail in the Liberal plan and the fact that it will lead to more deficit spending without a clear indication of how it would create jobs.

Mr. Sohi promoted the government's plan this week at a conference in Toronto organized by The Canadian Council for Public-Private Partnerships.

In an interview, Mr. Sohi said the government is still working on the details of the infrastructure bank and any decisions on user fees such as road tolls will be up to municipalities and provinces.

"As proponents and owners of the projects, they determine whether to charge a price for use of the infrastructure or not. That's their decision. We don't get involved in that discussion and we don't want to get involved in that discussion."

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Meanwhile in New York, Steven Mnuchin, a member of Mr. Trump's transition team, told reporters on Wednesday that a federal infrastructure bank in the United States is under consideration. Mr. Trump has promised a major increase in infrastructure spending though partnerships with the private sector, and criticized Democratic candidate Hillary Clinton during the campaign for promoting an infrastructure bank.