Lawyers for Mohamed Zeki Mahjoub, whom Ottawa deems a threat to national security, argue his right to fair process has been irrevocably damaged.
To continue trying to deport Mahjoub, his lawyers argue, violates his rights and would bring the justice system into disrepute.
"The technical term is a 'mess'," the lawyers state in new submissions to Federal Court.
"All of the king's horses and all the king's men cannot put this Humpty Dumpty situation back together again."
Mahjoub has been fighting his national security certificate, which was first imposed in 2000, as unreasonable.
Based partly on secret evidence he has never seen, Ottawa maintains he was a ranking member of a militant Egyptian terrorist organization. Canada has been unable to deport him because of the likelihood he could be tortured.
Last summer, the Dept. of Justice mistakenly took documents belonging to his counsel from a special room at the court building in Toronto.
Among other things, the material related to his lawyers' legal strategy, his and their handwritten notes, and their preparations for cross-examining witnesses, including a lead analyst for Canada's spy agency.
In response, Federal Court Judge Edmond Blanchard ordered the two sides to sort out what documents had been taken, saying he would then hear submissions on the harm caused.
Mahjoub's lawyers argue the separation process only made things worse.
They say the government has breached two fundamental tenets of the justice system: solicitor-client privilege and litigation privilege.
By doing so, they argue, the government has gained a grossly unfair advantage in the proceedings and the only remedy is to put a stop to them permanently.
"Each of these documents individually helps to understand the thought processes of (Mahjoub's) counsel, the strategy and/or the means by which that strategy will be implemented," his lawyers say in court filings.
For its part, the government argues its "review" of the files was "superficial" and resulted in no serious or ongoing prejudice to him.
Ottawa also maintains it is in society's interests to continue its case. The government insists Mahjoub still has extremist beliefs and remains a threat to public safety despite having had no contact with former associates for 16 years.
The 51-year-old father of three came to Canada in 1995 and was granted refugee status in 1996.
He was arrested in Toronto in 2000 and held on a national security certificate, which allows the government to detain non-citizens indefinitely without charge or trial pending deportation.
A new certificate was issued against him in 2008 after the Supreme Court of Canada threw out the original regime as unconstitutional.
Documents obtained earlier by The Canadian Press show Canada's spy agency conceded several years ago that most of its evidence was derived from sources linked to torture. The intelligence service has also admitted to listening in on his calls with his lawyers.
Mahjoub remains under house arrest in Toronto, although some of the most onerous conditions were eased in February.
Of four other Muslim men similarly branded as threats to Canada, two have successfully challenged Ottawa's case.
Two others, Algerian Mohamed Harkat in Ottawa and Egyptian Mahmoud Jaballah in Toronto, are still fighting.