Western diplomats in Beijing, however, say the cases are a tit-for-tat reprisal.
Canadian Prime Minister Justin Trudeau said in Ottawa that he is concerned that China chose to "arbitrarily" apply the death penalty to a Canadian citizen.
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.
Schellenberg had originally been sentenced to 15 years in prison and a 150,000-yuan ($22,000, €19,300) fine in November.
He appealed against the sentence to the Liaoning High People's Court, where prosecutors argued the sentence was too lenient.
China's abrupt retrial of Schellenberg "is suspicious, to say the least", tweeted Roland Paris, a University of Ottawa professor of worldwide affairs and a former adviser to the Trudeau government.
Schellenberg's fate is likely to become a volatile factor in diplomacy between Beijing and Ottawa after Canadian authorities arrested a Chinese tech executive last month.
The sentence comes against the backdrop of Beijing's anger over the arrest in Canada of a top executive from telecom giant Huawei last month on a United States extradition request related to Iran sanctions violations. She is out on bail in Canada and awaiting a bail extradition proceeding next month.
Schellenberg will have the right to appeal the sentence, according to Reuters.
He has 10 days to appeal.
Beijing has repeatedly denied any diplomatic pressure in the case.
Prime Minister Justin Trudeau said the sentence was a case of China "choosing to act arbitrarily" and added that China was refusing to follow global principles.
Two Chinese men have also received sentences - one to life imprisonment, while another was handed a suspended death sentence.
Courts heard an appeal of that conviction on December 29, 2018, and ordered a retrial for Monday, raising the possibility of a harsher sentence.
"I would suggest the Canadian study the Vienna Convention before making such a comment, so as not to be inaccurate and make oneself a laughing stock", Hua said, in response to a question about Trudeau's remarks.
Trudeau said last week that Chinese officials were not respecting Kovrig's diplomatic immunity.
Persons carrying a diplomatic passport are protected by limited immunity when they are overseas under the terms of the Vienna Convention. "I suggest that the relevant Canadian person carefully study the Vienna Convention on Diplomatic Relations and global law before commenting on the cases, or they would only expose themselves to ridicule with such specious remarks". One week later, two Canadian nationalswere detained in China on suspicion of "engaging in activities harming China's national security".
"Since the December 1st arrest of Ms. Wanzhou, Canada has been subject to retaliatory detentions by the Chinese government".
The Canadian citizen was first detained in 2014 following a drug trafficking investigation.
Canada has embarked on a campaign with allies to win the release of Kovrig and Spavor. She faces possible deportation to the United States. Trudeau called U.S. President Donald Trump about their case last week and the White House called the arrests "unlawful". On Friday, China protested Poland's arrest of a local former Huawei employee over spying allegations.