The Canadian court said handing over the documents to the United States meant Canada had "participated in a process that was contrary to Canada's international human rights obligations."
In a unanimous decision, the court said Khadr was entitled to see at least some of the documents that Canada gave to the United States to help him prepare for his trial at the US naval base in Cuba in late summer or early fall.
Khadr, the only Western prisoner still held at the Guantanamo Bay prison, faces charges of throwing a grenade that killed an American soldier and wounded another during a fight at an al Qaeda compound in Afghanistan in 2002.
Officials of the Canadian Security Intelligence Service (CSIS) interviewed Khadr at Guantanamo the following year.
Now aged 21, Khadr was 15 at the time of the fight and his supporters say Canada should push the United States to allow him to return home. The Canadian government has refused, saying Khadr has been charged with a serious crime.
The Canadian court relied on US Supreme Court decisions made in 2004 and 2006 on the Guantanamo process to conclude that Canada had participated in a process that violated the Geneva Conventions and US law.
"The violations of human rights identified by the United States Supreme Court are sufficient to permit us to conclude that the regime providing for the detention and trial of Mr. Khadr at the time of the CSIS interviews constituted a clear violation of fundamental human rights protected by international law," Friday's decision said.
It stopped short of declaring the current set-up at Guantanamo, as amended by the Bush administration after the US decisions, to be illegal. But Khadr's legal team nonetheless characterized it as such.
"Whether or not we get additional documents, Omar Khadr will not receive a fair trial from a Guantanamo Bay military commission," said Lt. Cmdr. William Kuebler, the US military lawyer representing Khadr.
"The more important aspect of this ruling is that the Canadian Supreme Court has now said, unanimously, that Guantanamo Bay violates international law. The only thing that can stop this ongoing injustice is prompt intervention by the Canadian government to bring Omar home to face due process under Canadian law."
The Canadian government had no immediate reaction to the ruling.
In a disappointment for Khadr, the court limited the documents to which he is entitled. He will see only material from the Canadian interviews and information passed on to the United States. He will not gain access to any and all documents that might help Khadr's legal team prepare its defense.
Another of Khadr's lawyers, Nathan Whitling, said he is seeking a report prepared by the US military on the events surrounding his arrest. He said Canada has it but is not obliged by the decision to produce it, and the US side says it can no longer find it.