Trudeau, in a wide-ranging interview airing Saturday on CBC Radio's The House, told host Evan Solomon he and Leslie, "had conversations but there was no active courting."
"He had a range of conversations with different people, different political parties, and I'm quite pleased that after reflection … he chose to serve his country through the Liberal Party," Trudeau said.
Leslie, who is widely expected run for the Liberal nomination in the Ottawa-Orléans riding, is currently serving as senior adviser to the Liberal Party on matters of foreign policy and defence.
The retired lieutenant-general was thrust into the spotlight this week after it was revealed that his move from one Ottawa home to another cost taxpayers $72,000.
Defence Minister Rob Nicholson immediately accused Leslie of "grossly excessive" moving expenses and promised to conduct a review.
Leslie said he simply accepted a standard benefit available to any veteran with 20 or more years of service that allows veterans a final move to anywhere in Canada.
Trudeau defended Leslie saying, "he followed all the rules."
And while that may be true, Nicholson said it was also "a matter of judgment."
Trudeau told Solomon that Leslie's 35 years of service with the Canadian Forces speaks for his judgment.
"I'm certainly not going to start questioning benefits to veterans who've served their country the way they did," Trudeau said.
While there may be a genuine need to review the military retirement benefit, Trudeau said that using Leslie's case as the basis for the review was inappropriate.
"I don't think its appropriate to start questioning veterans' benefits on the basis of a partisan political attack."
Trudeau says Liberals would not raise taxes
While Trudeau has yet to present an economic agenda, he told Solomon a Trudeau-led government would not raise personal or corporate taxes, nor increase the GST.
"Canadians are struggling … There is no reason to raise taxes on them now. We are not going to be raising taxes," Trudeau said.
He accused the Conservative government of using the federal budget as "election posturing."
"The balance that they're coming to, supposedly, is all about positioning themselves for an election and is not about the interests of Canadians or the country."
Trudeau, who supports the $7-billion proposed Keystone XL pipeline, blamed Prime Minister Stephen Harper and his government's lack of environmental regulations in the oil and gas sector for the deteriorating relationship between Canada and the United States.
"I think what's had an impact is Mr. Harper's unwillingness or inability to do anything responsible on the environmental file … that would give [U.S.] President Obama and Canadians in general reassurance that this government is not mortgaging our futures by being irresponsible around the environment," he said.
On the situation in Ukraine, Trudeau said Canada could impose financial sanctions on President Viktor Yanukovych and his allies. "Hitting him in his pocket book is something that Canada can lead the charge on."
Trudeau said the greatest challenge going forward is to grow his team and get more MPs elected in the next federal election in 2015.
"Regardless of the momentum and of money coming in, we have a very small caucus right now at 36 people. We have a lot of work to do," Trudeau said.
The Liberal Leader and his wife Sophie Grégoire are expecting their third child. While the due date is one week to 10 days away, Trudeau said, "it could be any minute."
Asked if they are expecting a boy or a girl, Trudeau said the couple has not asked.
"We have a boy and a girl, so we are looking forward to a wonderful surprise," Trudeau said.
The Liberal convention in Montreal runs through the weekend with a keynote speech by Trudeau on Saturday night.
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