Khadr was immediately whisked off to a maximum-security facility in eastern Ontario following the five-hour flight to CFB Trenton, Ont.
"He's finding it hard to believe that this has finally happened," John Norris, one of Khadr's lawyers, told The Canadian Press just after speaking to his client by phone.
"His spirits are good. He is very, very happy to be home."
Under a plea agreement, the Toronto-born Khadr was eligible to return to Canada a year ago to serve out the remainder of an eight-year sentence for war crimes handed down by a much maligned military commission in October 2010.
But his politically-wrought transfer was delayed amid sniping between Canada and the U.S., while Public Safety Minister Vic Toews insisted he needed to satisfy himself that Khadr, who turned 26 earlier this month, would pose no threat to public safety.
"Omar Khadr is a known supporter of the al-Qaida terrorist network and a convicted terrorist," Toews said Saturday, repeating a standard government line.
"(But) I am satisfied the Correctional Service of Canada can administer Omar Khadr's sentence in a manner which recognizes the serious nature of the crimes that he has committed, and ensure the safety of Canadians is protected during incarceration."
In his three-page decision Friday allowing the transfer, Toews identified five areas of concern, including that Khadr has been away from Canadian society for years and will require "substantial management" to re-integrate.
Toews also said Khadr idealizes his late father — a purported high-ranking al-Qaida financier — while his mother and older sister "have openly applauded his crimes and terrorist activities," an apparent reference to media comments they made eight years ago.
Still, Toews said it is up to the parole board to determine how many of the six years remaining on his eight-year sentence Khadr will have to serve behind bars.
The inmate is eligible for early release within months and the minister said he was counting on the board to put "robust conditions" in place if it does allow him out.
Norris, who said the transfer was "finally a time that justice had triumphed over politics," expressed surprise at Toews' position.
"We're at a loss to understand why the government continues to demonize Omar and to stoke public opinion against him," said Norris.
"We know him to be a kind, intelligent, thoughtful young man who has tremendous potential and we know that he will live up to that."
Khadr was taken upon his arrival in Canada to Millhaven Institution just west of Kingston, Ont., for assessment pending permanent placement.
News their relative was back in Canada caught Khadr's family in Toronto off guard.
"Do we know where he is so we can maybe go see him?" one close relative asked a reporter.
In October 2010, Khadr pleaded guilty to five war crimes committed as a 15 year old in Afghanistan.
The most serious offence was murder in violation of the rules of war — a crime not recognized outside of the military commissions — for the death of Sgt. Christopher Speer. The U.S. special forces soldier was killed by a grenade Khadr admitted throwing following a massive bombardment of the compound he was at in July 2002.
Khadr, near death and almost blind, was found in the rubble and taken to Bagram prison in Afghanistan. He was transferred a few months later to Guantanamo Bay.
In exchange for his guilty plea, the 40-year sentence handed him by a military-commission jury was capped at a further eight years, with only one more to be served in Guantanamo, but he remained there until Saturday.
Ottawa blamed the Americans for failing to authorize the transfer, while the Americans and Khadr supporters fumed that Canada was dragging its feet.
In Ottawa, Liberal Leader Bob Rae called it "extremely unfortunate" the Conservative government took so long to allow Khadr back.
NDP foreign affairs critic Paul Dewar said the Conservatives had tried to look like they were being tough on terrorism but had undermined Canada's international credibility in the process.
He urged the government to let prison and parole authorities take over.
"There should be absolutely no interference politically with this case," Dewar said.
Social media and online sites showed the same kind of split that has long characterized Canadians' views on Khadr, with most comments slamming his return.
"The only embarrassment here is that this piece of trash was allowed to return home to our wonderful country," one poster wrote on a news site.
"I am so sorry to see this traitor back in our country — this is one of the sad prices we pay to live in a democracy but it is another testimony to our greatness," another said.
Supporters were also quick to express their opinions.
"We treat child soldiers from other countries with compassion but this man, who was also a child soldier brainwashed by his own parents, we treat with a complete lack of understanding and hatred," one said.
The Pentagon had little comment, saying the U.S. "co-ordinated with the government of Canada regarding appropriate security and humane treatment measures."
Khadr was the last westerner and youngest inmate held at the U.S. prison in Cuba.
Human rights groups, which have long condemned Khadr's incarceration and treatment, applauded the transfer.
The New York-based Centre for Constitutional Rights said the move ended "one of the ugliest chapters" in the Guantanamo's history and called for Canada to release him immediately.
In Washington, Human Rights Watch called on Ottawa to help the "former child soldier" integrate into society and "remedy abuses he suffered" during his decade in U.S. custody.
"Omar Khadr's repatriation provides an opportunity for Canada to begin to right a wrong," the organization's Andrea Prasow said.
"Canada should also do all it can to hold accountable those who are responsible for his abuse."
Among other things, Khadr was shackled in stress positions, threatened with rape and deprived of sleep during some of his years in custody.
The Supreme Court of Canada twice ruled the government violated his rights.
Khadr's only public words since his capture came at his military commission trial, when he apologized to Speer's widow and said his "biggest dream" was to get out of Guantanamo and said he hated no one.
"Love, forgiveness are more constructive and bring people together."
Also on HuffPost