The Crown is asking the Supreme Court of Canada to review an Ontario Court of Appeal's decision to order a new trial for two men convicted of plotting to derail a Via Rail passenger train in the Greater Toronto Area.

In a written submission to the high court, federal lawyers say the Court of Appeal overturned the convictions on the basis of a "highly technical error" in the jury selection process that did not interfere with the fair-trial rights of either man.

Raed Jaser and Chiheb Esseghaier were found guilty in 2015 on terror-related charges arising from an al-Qaeda-inspired plot to derail a passenger train travelling between New York City and Toronto, operated by U.S. rail service Amtrak south of the border and Via Rail in Canada. Both were sentenced to life in prison.

In August, the Appeal Court ordered a fresh trial for the men on grounds the jury that convicted them was improperly chosen.

Following the decision, the Public Prosecution Service of Canada said it would proceed with a new trial, but noted it had 60 days to decide whether to seek permission to appeal from the Supreme Court.

In the submission, the federal lawyers note Jaser and Esseghaier were convicted of the most serious terrorism offences in Canadian law after nearly nine months of pretrial motions and a three-month jury trial.

"Overturning these convictions on the basis of a technical error that had no appreciable effect on the conduct of the trial is a triumph of form over substance," the submission says.

"Where, as here, there is no actual demonstrable prejudice to the fairness of the trial, the verdict properly reached by the trier of fact after a long and arduous trial should not so easily be set aside."

SCC has to decide if it will hear the matter

Jaser and Esseghaier will also have an opportunity to make submissions to the Supreme Court, which is likely to rule on whether to hear the matter some time next year.

Before the terror trial, the case's high profile and the fact the two accused were Muslim and members of a visible minority meant that prospective jurors were asked about their ability to be impartial.

Historically during this process, two people were given the role of "triers" who listened to the answers for signs of bias. Lawyers for the Crown and defence then decided whether to allow the individual to sit on the jury.

The use of "rotating triers" entailed having each newly appointed juror replace one of the two triers for subsequent questioning.

Counsel for Jaser wanted the challenges to proceed with rotating triers, with the other prospective jury members excluded from the room. Esseghaier was unrepresented, as he rejected the criminal justice system on religious grounds.

Due to changes to the law in 2008, there was uncertainty as to whether the procedures Jaser requested were even still available, and the judge eventually approved another method set out in the new statute.

Both men appealed their 2015 convictions. Counsel for Jaser and a court-appointed representative for Esseghaier argued the jury was improperly constituted.

In its August ruling, the Appeal Court said Jaser was improperly denied his preferred option for jury selection. The court also said if Jaser should have a new trial, Esseghaier was also entitled to one.

In their submission, the federal lawyers say the implication of allowing the appeal-court decision to stand extends beyond the case at hand.

"As the law currently stands, a reasonable error by a trial judge on a disputed issue related to jury selection can and will invalidate the trial that follows, regardless of any prejudice."