Sebastian Burns and Atif Rafay argued their convictions for the July 1994 slayings of Rafay's family should be thrown out because much of the evidence was from a so-called Mr. Big sting called Project Estate conducted by the RCMP.
Lawyers for Burns and Rafay argued details from such stings are not admissible in U.S. courts and the men, who were 18 at the time of the killings, were coerced into admitting to the murders.
Vancouver radio station CKNW quoted a lawyer for the pair, David Koch, as saying he would appeal the decision.
The panel of three judges has ruled proper U.S. legal standards were applied in accepting the sting evidence and that a lower court was right to decide Burns and Rafay confessed voluntarily.
"Viewed in their entirety, the circumstances in the case, including the defendants' private conversations, their participation in the scenarios leading up to the confessions, and their conduct and statements during the confessions themselves, indicate that Project Estate did not vitiate the defendants' ability to make independent or rational decisions or otherwise overcome their will," the judges said in their written ruling.
Hours of audio and video recordings made in the men's house and during various scenarios provide a "uniquely rich context for assessing the effect of the undercover operations on the defendants."
The ruling noted that after the pair became the targets of the RCMP investigation, they were led to believe they were entering a lucrative criminal organization.
Undercover RCMP officers got Burns to confess to the killing through a ruse asking for the murder details in order to destroy evidence that could point to him.
Rafay and Burns claimed they falsely confessed to the murders for fear the officers posing as criminals would kill them if they said they did not commit the crimes.
But, the ruling said, "Burns's actions throughout (the undercover investigation) suggest deliberate attempts to impress (the officer), not fear of physical injury."
Burns and Rafay are each serving three consecutive life terms for the murders, but have been spared the death penalty because of an extradition arrangement that returned them to Washington state in 2001.
Lawyers for the two also argued their right to a speedy trial was breached because U.S. authorities held up their extradition by not agreeing to abstain from pursuing the death penalty right away.
The court rejected that argument as well, pointing out they had not raised the issue until 1999, well after their arrest.
The men became friends while attending high school in West Vancouver and the jury at the men's six-month trial was told Rafay was motivated by money and planned the slayings while Burns carried them out.
The two men, who'd been visiting Rafay's family in Bellevue, Wash., told police they returned to the house at about 2 a.m. on July 14, 1994 and found Rafay's relatives dead after an apparent break-in.
They returned to Vancouver a few days later without attending the family's funeral.
The duo has also been in the news for issues with their legal defence.
Burns made headlines in 2002 when his lawyer Theresa Olson was removed from the case after prison guards claimed to have seen the two having sex during a visit.
The same year, The Seattle Post Intelligencer reported a rift between lawyers representing the two defendants that resulted in a complaint to the Washington Bar Association and a no-contact order.
The details of the complaint are in sealed files.