They filed a notice of application Friday seeking to ask the Federal Court to review the federal government's failure to ask the U.S. to transfer Khadr to Canadian custody.
"The delay in this matter is utterly unconscionable in the circumstances of this case," Brydie Bethell, one of Khadr's Canadian lawyers, said in an email.
Khadr has been serving an eight-year sentence at the American military prison at Guantanamo Bay in Cuba since he pleaded guilty to war crimes in 2010.
But Khadr, 25, was eligible for transfer back to Canada last October and the Harper government has offered little explanation as to why it hasn't made a request, only saying a decision would come in due course.
The war crimes that Khadr was charged with include the killing of a U.S. army medic in Afghanistan in 2002. He was 15 years old at the time.
Under a plea-bargain deal he was only expected to serve one year of his sentence at Guantanamo Bay, where he had been held for years before his trial.
One of Khadr's U.S. lawyers said last month he has been told American officials can't understand Canada's reluctance to ask that Khadr be returned home.
Lt.-Col. Jon Jackson said U.S. officials are frustrated by the delay of the return of the last Western national to held at the much-maligned U.S. military prison.
U.S. Defence Secretary Leon Panetta signed off of Khadr's transfer in April, he added.
A U.S. Embassy spokesman said last month that the American and Canadian governments have been in regular contact on the case but refused to speculate about transfer timelines.
If the Federal Court agrees to review the case it could direct the federal government to make a decision on the transfer case, Bethell said, adding the court would look at all the circumstances to determine whether the delay in making the transfer request is unreasonable.