Canadian Foreign Minister Chrystia Freeland says Canada has formally asked China to spare the life of a Canadian man facing a death sentence.
Ms Freeland also mentioned a long list of allies that the country has courted in its efforts to free two other Canadians imprisoned last month after Canada arrested a Chinese executive at the request of the United States.
Her remarks came after China expressed "strong dissatisfaction" with Canadian Prime Minister Justin Trudeau's criticism of a death sentence handed down to a previously-arrested third Canadian.
Monday's death sentence by a Chinese court on Canadian Robert Schellenberg for allegedly conspiring to smuggle 222kg of methamphetamines from China to Australia in 2014 has become the latest strain on ties.
Ms Freeland said the death penalty is inhumane and inappropriate, and Canada has asked China's ambassador to Canada for clemency.
China denounced Canada on Tuesday for "irresponsible" remarks after Canadian Prime Minister Justin Trudeau accused it of "arbitrarily" sentencing a Canadian to death for drug smuggling, aggravating already icy relations.
The countries have been at odds since early December, when Canadian police arrested Meng Wanzhou, chief financial officer of Huawei Technologies Co Ltd, on a US extradition request as part of an investigation into suspected violations of US trade sanctions.
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Days later, China detained two Canadians on suspicion of endangering state security.
China has not linked any of the three Canadians' cases to Meng's arrest but has warned of severe consequences if she was not immediately released.
Trudeau said it should be of "extreme concern" to Canada's allies, as it was to his government, that China had chosen to "arbitrarily apply" the death penalty.
Chinese Foreign Ministry spokeswoman Hua Chunying expressed "strong dissatisfaction" with that.
"The remarks by the relevant Canadian person lack the most basic awareness of the legal system," Ms Hua told reporters.
Taking Canada to task for issuing an updated travel advisory warning citizens about the risk of arbitrary enforcement of laws in China, Hua said Canada should instead remind its people to avoid drug smuggling.
"We urge the Canadian side to respect the rule of law, respect China's legal sovereignty, correct its mistakes, and stop making irresponsible remarks," Ms Hua said.
China later issued its own travel warning, citing the "arbitrary detention" of a Chinese national in Canada.