The upgraded warning comes after a Canadian man had his accessory to drug smuggling sentence upgraded from 15 years to a death sentence.
On Monday, a Chinese court sentenced Robert Lloyd Schellenberg to death, overturning a 15-year prison term handed down earlier.
"It is of extreme concern to us as a government, as it should be to all our worldwide friends and allies, that China has chosen to begin to arbitrarily apply the death penalty in cases facing, as in this case, facing a Canadian", Trudeau said in a news conference following Monday's ruling.
China also seized two Canadians, Michael Kovrig and Michael Spavor, on national security grounds as the government in Beijing complains about Canada's arrest of Huawei Chief Financial Officer Meng Wanzhou in Vancouver.
Schellenberg's case was the most recent in a series of incidents between Canada and Beijing, which began with Meng's arrest at the request of the US.
The advice states that citizens should "exercise a high degree of caution in China due to the risk of arbitrary enforcement of local laws".
"I think Canada's travel warning is like "thieves yelling out thieves" because it is actually Canada, not China, that has arbitrarily detained a foreign citizen based on so-called legal reasons", she said. But during the retrial, the court sided with the prosecution, which claimed to have uncovered new evidence proving Schellenberg's principal role in the case.
"It is of extreme concern to us as a government, as it should be to all our global friends and allies, that China has chosen to begin to arbitrarily apply (the) death penalty.as in this case", Trudeau told reporters in Ottawa.
Schellenberg's defense lawyer, Zhang Dongshuo, said his client plans to appeal the verdict. We are all very heartbroken right now and we are all in shock.
The move appears to be the latest in an escalating feud that began with the arrest of the Huawei executive Meng Wanzhou in Canada in early December at the request of the United States, which has accused her of violating sanctions. She called on the Canadian government to release Meng.More news: White House Pulls Fast (Food) One on NCAA Football Champs
Guy Saint-Jacques, Canada's ambassador to China from 2012 to 2016, said he believes China is making an example out of Schellenberg.
Canada has embarked on a campaign with allies to win the release of Kovrig and Spavor. The decision to appeal the first ruling came back to haunt Schellenberg as a Liaoning People's Court prosecutor argued the initial sentence was too lenient.
According to China's Criminal Procedure Law, an execution should be carried out within seven days of the lower court receiving notice that the Supreme People's Court has approved the death sentence.
Noting that Chinese authorities handled the case according to law, Foreign Ministry spokesperson Hua Chunying said that no matter which point of view you take, the former Canadian diplomat Michael Kovrig does not enjoy diplomatic immunity stipulated in the Vienna Convention on Diplomatic Relations.
"The Schellenberg family requests that all Canadians stand with us and pray for the safe return of our loved one", the statement said.
Beijing has not drawn a direct link between the detentions and the arrest of Meng, wanted by United States authorities for allegedly misleading multinational banks about Iran-linked transactions.
Mr Brown said Schellenberg was struggling with addiction.
Schellenberg was accused of trying to smuggle more than 222 kilograms of methamphetamine from China to Australia. We want to keep our journalism open and accessible and be able to keep providing you with news and analyses from the frontlines of Israel, the Middle East and the Jewish World.
The episode was terribly damaging to relations between the United Kingdom and China, said Ben Rowswell, a former diplomat and current president of the Canadian International Council, a non-partisan think-tank.
"Anyone with normal judgment can see that the Meng Wanzhou case is not a normal legal case, and the detention of Meng Wanzhou is not just".