"Our position has not changed and it's not going to. We're not going to blow in the wind on something as fundamental as this," Kory Teneycke, Harper's chief spokesman, said.
"Making a change at the 11th hour because his legal team is pursuing an aggressive media strategy is not in the interests of due process ... We're about doing what the right thing is," he said.
Khadr was taken to Afghanistan by his father Ahmed Said Khadr, who is alleged to have financed al-Qaeda, as well as being an associate of Osama bin Laden.
Khadr senior was killed in a battle with Pakistani forces in 2003.
"I am suffering but I am holding [on] because I know there are other hundreds who are suffering like Omar and I wish I could do something," Maha Elsamnah, Khadr's mother, said on Tuesday.
"If they think Omar would need rehabilitation I would love it and I know Omar would need rehab. Omar will need somebody to reassure him that he still deserves to live," she said.
Jonathan Kay of the National Post newspaper, which is a strong supporter of Harper, said Khadr should be allowed to come home.
"Millions of people [around the world] are now wondering why Canada's government has acquiesced - and as the video shows, even participated - in the unconscionable treatment of a blubbering boy soldier," he wrote on Wednesday.
Layne Morris, a US army sergeant who was injured in the July 2002 battle that ended with Khadr's capture, said the Canadian interrogators should have been tougher on Khadr.
"I think Omar is where he belongs. I hope he stays there for a good long time ... as long as he's a danger to either the United States or Canada or any kind of western civilisation," he told the Canadian Broadcasting Corporation.