That provincial agency is part of the Parti Quebecois effort at so-called "sovereigntist governance" to winnow powers away from Ottawa. The government has launched a study of the project, and appears poised to demand that Ottawa hand the province its share of the federal aid budget.
Mulcair acknowledged the frustration that some might feel with the development policies of the Harper government. But he didn't express support for the PQ effort.
"It's easy to understand how some provinces, realizing how far we've gone away from our work in terms of international solidarity, want to try to fill that void themselves," the federal Opposition leader said after a foreign-policy speech on Thursday.
"My goal is not to see that done individually but to have it done by a Canadian government for and behalf of all Canadians."
In his speech, Mulcair painted a bleak picture of federal efforts internationally that he said contrasted vividly from the honest-broker role of Canada in years past.
Where the Canadian government had been focused on spreading peace, social justice and prosperity in the past, he said that under the federal Conservatives were now more preoccupied with advancing partisan interests.
His complaints were similar to those expressed on Wednesday by Quebec International Relations Minister Jean-Francois Lisee.
Lisee announced in Quebec City that the provincial government is looking at how to set up it own version of the Canadian International Development Agency, saying the federal incarnation no longer reflects Quebec values under the Tories.
Lisee said federal aid programs had become tainted by the priorities of the federal Conservative party, as the Harper government increasingly wants to pair aid efforts with mining projects abroad.
On Thursday, Mulcair said the government had to better reflect Canadian values.
"My first hope would be that the Canada the Conservatives project onto the world stage would begin to resemble Canadians," Mulcair said after a speech to the Montreal Council on Foreign Relations.
"We've always been an open, caring, respectful people playing a very important role on the world stage. The Canada that Stephen Harper is projecting onto the world stage is unrecognizable to the world and unrecognizable to ourselves."
But pressed on whether he agreed with the efforts of Premier Pauline Marois' government, Mulcair was less specific.
"I'm in agreement with Canadians from one ocean to the other who want to work towards a vision for a progressive nation," he said. "My work as a leader of the NDP and leader of the official Opposition is to replace Stephen Harper with a government that is reflective of those values."
The Prime Minister's Office has already rejected the Quebec initiative, saying that foreign policy is an area of federal jurisdiction under the Constitution.
But questions that touch on Quebec nationalism are more politically sensitive for Mulcair. His NDP caucus comprises nearly five-dozen Quebec MPs, many of whom were elected in ridings that were longtime Bloc Quebecois fortresses.
He has been mostly careful to avoid delving into issues that could pit his Quebec supporters against voters in the rest of the country.