Canada will "implement" a plea deal between the U.S. government and Omar Khadr to allow the convicted war criminal to return to Canada after serving one year at Guantanamo Bay, Foreign Affairs Minister Lawrence Cannon says.

In this Pentagon-approved sketch by artist Janet Hamlin, Omar Khadr listens to closing arguments Saturday in Guantanamo Bay, Cuba. (Canadian Press)

Under fire from opposition MPs during Monday's question period in the House of Commons, Cannon insisted the Canadian government was not involved in plea negotiations, despite a U.S. State Department memorandum that reveals the Conservative government was aware of the Toronto-born Khadr's plea agreement.

Responding to a question from Bloc Québécois Leader Gilles Duceppe, Cannon said in French that Canada did not participate in the discussions on Khadr's sentence.

Liberal MP Ujjal Dosanjh accused Cannon of deliberately misleading Canadians on the government's involvement. "Obviously they were talking to the U.S. government all the time," Dosanjh told the House.

Shortly before Cannon spoke, a State Department spokesman in Washington said an exchange of diplomatic notes on Oct. 23 "helped pave the way" for the plea bargain. But Cannon quoted the chief prosecutor at the tribunals, navy Capt. John F. Murphy, as saying the plea deal was solely between the U.S. and Khadr's lawyers.

'Perfectly clear' Canada made deal: Ignatieff

NDP MP Wayne Marston said the memorandum shows that either Cannon doesn't know what's going on in his own department or was disingenuous in his statements to the Commons.

"The documents lay out the fact that his department was aware of what was going on with Khadr and agreed with the plea deal, and he said in the House that wasn't the case," Marston told CBC News on Monday on Parliament Hill.

Speaking on Monday during a visit to Gaspésie, Que., Liberal Leader Michael Ignatieff said it's "perfectly clear" the Canadian government reached a deal with the U.S. on Khadr.

"Why wasn't the government of Canada willing to say so in the House of Commons?" Ignatieff told reporters.

"This kind of behaviour makes Canadians ask themselves, 'Well, if they can't tell us the truth about the Khadr affair, can they tell us the truth about anything else?' "

8-year sentence cap

Khadr, now 24, was sentenced Sunday to 40 years in prison for war crimes, including the murder of a U.S. soldier in Afghanistan in 2002.

But the decision by a U.S. military panel was largely symbolic, as a pretrial plea deal capped Khadr's sentence at eight years, with the first year to be served at the American naval base detention centre.

According to the State Department memorandum, Canada and the United States exchanged two diplomatic notes on Oct. 23, two days before Khadr pleaded guilty to five charges including the murder of Sgt. 1st Class Christopher Speer during a battle in Afghanistan in July 2002, when Khadr was 15 years old.

The Canadian Embassy in Washington said in a memo dated Oct. 23 that the Canadian government "is inclined to favourably consider" a request for a transfer to Canada for Khadr to serve the rest of his sentence after another year at Guantanamo, where he has been in custody since 2002.