The court ruled that Khadr, now 21, should have some access to the intelligence documents to aid his defence at his upcoming military tribunal.
Canada had "participated in a process that was contrary to [its] international human rights obligations" when it gave US officials the results of the interviews, it said.
Khadr is charged with murder, conspiracy and other offences in a trial scheduled to begin later this year.
The court said exceptions would apply to any documents that could compromise national security and said a judge would have discretion over which documents would be made available to Khadr's lawyers.
It did not directly pass judgment on whether the detention process at Guantanamo Bay and the military tribunals set up to try foreign-born suspects were a violation of human rights.
However, it noted the US Supreme Court had found the Guantanamo Bay legal processes "to violate US domestic law and international human rights obligations to which Canada subscribes".
"The principles of international law ... which normally require that Canadian officials operating abroad comply with local law, do not extend to participation in processes that violate Canada's international human rights obligations," the court ruled.
Nick Spicer, Al Jazeera's correspondent in Ottawa, Canada, says that Khadr's defenders are happy they have won both a moral victory and the ability to better defend their client.
But many Canadians are wondering why their government has not done more to secure Khadr's release, given that he was a youth when arrested and is the only Westerner thought to still be held at the US facility, he said.
Khadr was arrested following a battle between suspected al-Qaeda forces in Iraq and US troops, in which the US alleged he killed a US health worker with a grenade.
He has previously claimed that he has been abused while being held at the US detention facility.
Canadian officials have said they accept US assurances that Khadr has been treated humanely, but human rights groups believe Canada has not done enough to ensure Khadr is being fairly treated.