With the 2015 election campaign unofficially underway, the Conservatives launched their third attack against Liberal Leader Justin Trudeau in less than seven days.

The Conservatives seized on Marc Emery's return to Canada to attack Trudeau over his position on legalizing marijuana, saying a Liberal government would make it easier for children to get their hands on pot.

A message posted by the Conservative Party's headquarters said: "Ex-con #MarcEmery is back in #Canada ready to kick off campaign for best 'bud' @JustinTrudeau."

Emery, the self-proclaimed "prince of pot," was prosecuted in the U.S. for selling marijuana seeds to American clients from his Vancouver-based company, Cannabis Culture. He arrived in Canada today after spending nearly all of his five-year sentence in a U.S. jail.

While Emery has vowed to gather support for a Liberal government ahead of the next federal election as a way to seek political revenge against the Conservatives for what he sees as their role in his extradition, the Liberals have distanced themselves from the marijuana activist and his wife.

Jodie Emery has said she plans to seek the Liberal nomination in the riding of Vancouver East riding.

Liberal spokesman Dave Sommer told CBC News last month the party "does not endorse the Emerys' plans in any way. They are not affiliated with the party and we haven’t had any hand in planning these events at all."

Asked for a comment on the latest attack against Trudeau, the Liberal Party stood by those remarks.

Defining Trudeau?

In their latest effort to define Trudeau ahead of next year's federal election, the Conservatives posted a message on Twitter linking through to a page calling on Tory supporters to keep Trudeau and Emery "out of power."

"Justin has admitted that he wants to legalize marijuana – and now he is getting support from convicted U.S. criminal and self-proclaimed 'prince of pot' Marc Emery."

Supporters are asked to add their names, email addresses, and postal code as a way to build on the party's database.

A video of Trudeau talking about his position on pot was also posted on the same page. A voice narrating the video said "Imagine: selling marijuana just like cigarettes and alcohol. Justin Trudeau: he's in way over his head."

"Help keep marijuana away from our kids," said a message following the video.

Earlier in the day, Public Safety Minister Steven Blaney issued a public statement linking Emery and his wife to Trudeau.

"Mr. Emery and his wife are strong supporters of Justin Trudeau's 'vision' to legalize marijuana, in fact, Mrs. Emery plans to run for the Liberals as a pro-pot candidate in 2015.

"While the Liberals would try to make it easier for our children to access marijuana, Canadians can count on our government to put forward policies that keep drugs off our streets and keep our families safe," Blaney said.

On Monday, the Conservatives attacked Trudeau over comments he made about a Liberal government not keeping the First Nations Financial Transparency Act in place.​

Last Wednesday, Trudeau was accused of sympathizing with terrorists more than three years after he visited a mosque that was later declared by the U.S. to be one of nine places worldwide where "known al-Qaeda members were recruited, facilitated or trained" more than a decade earlier.

Trudeau has also been attacked for his comments on foreign policy and abortion.

He was not available for comment today.