The interview, which was resurrected in news reports, was seized upon by the federal Conservatives, who were quick out of the gate in defining previous Liberal leaders Stephane Dion and Michael Ignatieff as either ineffective or political tourists when they got their party's top job.
"You know what, we'll see what they dig up," the son of former prime minister Pierre Trudeau said Monday in an interview in the waning moments of a meet-and-greet in a posh Old Montreal hotel named for renowned Quebec poet Emile Nelligan.
"I'm me and I know where my values are and I know my connections with Canadians. We'll let them try and throw mud at me. I'm not going to do that, I'm not going to engage in that, I'm not going to start attacking Mr. Harper for comments he might have made or anyone else.
"People are tired of that. That's not where I'm going."
Conservatives quickly portrayed Dion as indecisive after he won the Liberal leadership in 2006. His successor, Ignatieff, was described as someone who only returned to Canada to seek the prime minister's job because it was in his own self-interest.
Political observers expect that Justin Trudeau is going to be under his political opponents' microscopes as the race heats up to lead the Liberals. He is an early favourite in the campaign which will conclude with a vote at a convention in Ottawa next April.
Trudeau has acknowledged that he has a reputation for speaking off the cuff and sometimes saying things that get him in hot water.
On Friday, he apologized for comments he made in a 2010 interview on the French-language Tele-Quebec station, where he blamed Canada's problems on Albertans controlling the "socio-economic" agenda.
He maintains however that the comments, which were resurrected a day earlier by Sun Media and latched onto by Conservatives, have been misinterpreted.
He says he was making a clumsy attack on Prime Minister Stephen Harper, who rose to power as a Calgary MP.
The kerfuffle didn't seem to have much resonance with supporters at Monday's event.
Michel Desjardins, 29, said he thinks Trudeau is genuine and has the type of values he wants in a leader.
"He's an inspiration for youngsters," said Desjardins, who is a Liberal party member. "He's definitely a reason I want to get involved in politics."
In his speech to more than 250 supporters who were also tapped for funds for his leadership bid, Trudeau said he wants to practice a style of politics different from the divisive approach that has emerged in Canada.
He said Canadians want their leaders to tackle fundamental issues like the economy, the disparity between rich and poor and key social issues such as the environment.
In a response to a question on legalization of marijuana laws, Trudeau said he is in favour of decriminalizing pot and taxing it.
"I think we should seriously look at legalization or taxing and regulation," he said after his speech. "I think it's the way to keep it out of the hands of our kids. I think it's a way of keeping the profits out of the criminal gang industry and I think it's an idea whose time has come.
"It just makes no sense to criminalize a segment of society for smoking pot anymore. I think we need to send clear messages that it's not good for you, but I think we should be mature enough as a society to allow people to make their own choices around marijuana and focus our efforts on other and more pressing issues."
Legal marijuana is being advocated by Vancouver MP Joyce Murray, who announced her candidacy for the Liberal leadership on Monday.
She has also called for the Liberals to co-operate with New Democrats and Greens in the 2015 election to beat Harper's Conservatives. That could include conducting run-off nominations to choose a single candidate in a tightly contested riding.
Trudeau said in an interview that Murray's idea is a non-starter if he becomes leader.
"I intend to run 338 candidates in the next election," he said, although he added that he welcomed Murray to the race.