Schellenberg was detained by Chinese authorities back in 2014, accused of being instrumental to drug smuggling within the country as well as having connections to global drug trafficking, the South China Morning Post reported.
Courts heard an appeal of that conviction on December 29, 2018, and ordered a retrial for Monday, raising the possibility of a harsher sentence. He was sentenced to 15 years in prison and fined $22,000.
At Schellenberg's appeal hearing last month, prosecutors said that emerging evidence indicated he had played a bigger role in a drug trafficking network and so his initial sentence was too light.
He was arrested along with Canadian entrepreneur Michael Spavor on vague national security allegations after a top Chinese executive with telecommunications network equipment giant Huawei was detained in Canada on December 1 at the request of Washington. The apparent weak evidence against the Canadian, the speed in scheduling a retrial, and China's invitation of the global press to cover the sentencing all indicate that the move could be retaliatory and aimed at gaining leverage over Ottawa.
The court was filled with about 70 observers who were patted down and made to empty pockets - receipts and stray coins were to be left at security.
Court retrials are rare in China and retrials calling for a harsher sentence are even rarer, said Donald Clarke, a George Washington University professor specialising in Chinese law. He said a friend recommended a man named Xu Qing as a translator.
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The crux of the retrial hinges on how much Schellenberg knows about the drug deal, which he claims was masterminded by Khamla Wong, a Canadian who was in 2016 arrested on drug charges.
But Chinese prosecutors said Schellenberg was the principal suspect in a case involving an global syndicate that planned to send some 222 kilogrammes (490 pounds) of methamphetamine to Australia.
Prosecutors presented Xu as a witness, who in almost two hours of testimony did not look at Schellenberg.
When pressed on details, he frequently said he could not remember and to refer to a written statement for details, including when Schellenberg questioned him about 180,000 yuan he was purportedly given.
A former oil worker, Robert Lloyd Schellenberg, was initially arrested back in 2015 on suspicion of smuggling more than 200 kilograms of methamphetamine into China. Canadian Prime Minister Justin Trudeau said he was concerned that China had decided "arbitrarily" to apply the death sentence in the case.
Beijing has repeatedly denied any diplomatic pressure behind Schellenberg's case. At a news briefing Friday, a spokesman for the ministry, Lu Kang, said critics should not undermine Chinese law for political purposes.
Before his arrest, Schellenberg had prepared to flee to Thailand from Dalian but was arrested while in transit in Guangzhou, the court said.