Garneau called the detentions "arbitrary" and said Canada is "deeply troubled by the lack of transparency surrounding these proceedings".
In Beijing, foreign ministry spokesman Zhao Lijian said "Chinese judicial organs handle cases independently in accordance with the law and fully guarantee the lawful rights of the individuals concerned".
The Global Times reported last week that the two men would "soon be tried" after they were charged with "crimes undermining China's national security" in June 2020.
Spavor, an entrepreneur with North Korea-related business, was charged with spying for a foreign entity and illegally procuring state secrets. Those convicted of serious violations of the section of law cited by Chinese authorities face sentences of between 10 years and life in prison.
Worldwide and bilateral treaties require that China provide Canadian diplomats access to the trial, but the court said Chinese law regarding trials on state security charges overrode such obligations, Nickel said.
Both men were formally charged with spying last June, after they were detained December 2018 in apparent retaliation for Canada's arrest on a U.S. extradition warrant of Huawei executive Meng Wanzhou days earlier.
Mr Kovrig, a former Canadian diplomat who worked for the International Crisis Group (ICG), is accused by the Chinese authorities of "stealing sensitive information and intelligence through contacts in China since 2017", while Mr Spavor, a businessman based in Beijing with a focus on North Korea, is accused of providing intelligence to Mr Kovrig.
In Vancouver on Thursday, Meng's lawyers told an extradition hearing Canadian officials abused their power when they conspired with the U.S. to arrest her. Defence lawyer Tony Paisana said Canadian Border Services Agency officers took Meng's phones, obtained their passwords, then handed them to Canadian police so the data could be shared with the Federal Bureau of Investigation.
Guy Saint-Jacques, a former Canadian ambassador to Beijing, said the timing was clearly created to coincide with the talks between the United States and China, which wants to pressure the Biden administration to arrange for Meng's release. "The message to Washington is that, 'If you want to help to get the Canadians back, you know what you have to do".
A Biden administration spokeswoman declined comment, referring only to President Joe Biden's previous remarks.
"Human beings are not bartering chips", Biden said after speaking with Trudeau by video link in February.
"We urge the USA side to correct its mistake without further delay and ensure Ms. Meng's safe return to China at an early date".
Chinese state media indicated last week that the trials could be imminent.
The legal tussle is expected to be raised at a meeting later Thursday in Alaska between U.S. Secretary of State Antony Blinken, national security adviser Jake Sullivan and top Chinese diplomats. "I was never given permission to talk to him", Garratt, who was released in 2016, said on CBC News Network's Power & Politics Thursday. In February, the cases led Canada to convene an global group opposing to the use of arbitrary detention as a coercive diplomatic tool, an initiative denounced by China as "hypocritical and despicable".
The trial on Friday took place after a rocky start to talks between top us and Chinese officials in Anchorage, marked by testy exchanges and barbs from both sides. Trudeau entered office in 2015 hoping to seal in trade deal with the world's second-largest economy.
Spavor's family have called for his unconditional release, insisting that he was innocent of the accusations.
"They shouldn't have been detained in the first place". A court hearing is scheduled Monday for Mr. Kovrig.