Prime Minister Justin Trudeau may want to focus on trade, tourism, and business opportunities during his trip to China, but there is a pressing problem threatening to knock him off his positive message.

He is facing growing pressure to resist entering free trade talks with China until a commercial dispute involving detained Canadians is resolved.

John Chang and his wife, Allison Lu, who own wineries in B.C. and Ontario, have been trapped in a diplomatic nightmare since they were arrested during a work trip to Shanghai in March of 2016.

The pair have been accused by Chinese authorities of smuggling after allegedly under-reporting the value of wine they export to Asia.

Lu has been released from custody but is not allowed to leave Shanghai, while her husband remains in a detention facility.

The couple's daughter, Amy Chang, said this is not a criminal matter and is demanding Trudeau hold off on free trade talks until her parents are sent back to Canada.

"When you're trying to negotiate a free trade agreement, especially between Canada and China, if you cannot protect your own citizens right now... there are more cases that are just going to come up," Chang said in an interview with CBC News.

The 24-year-old said the matter is urgent, since her father's health is declining. She said her father has two tumours on his liver.

"Justin Trudeau, I really hope this time when you go to China, I really hope you can bring my parents home for Christmas," Chang added.

Case raised at highest levels

Government officials would not confirm whether Trudeau plans to bring the Chang case up during high-level meetings with Chinese President Xi Jinping and Premier Li Keqiang.

But International Trade Minister Francois-Philippe Champagne told CBC Radio's The House that Canadian officials raise the case "all the time."

"I made sure this was understood by our Chinese counterparts that this is something that not only matters to me, but to the highest level of the Canadian government. I will continue to press for that," Champagne said.

International Trade Minister Francois-Philippe Champagne says Canada has pressed the Changs' case at the highest levels and will continue to do so. (Adrian Wyld/Canadian Press)

While he would not say if the Chang and Lu case is a deal-breaker for entering free trade talks, Champagne said Canada is committed to finding a resolution.

"I would say, what Canadians expect of us is to raise consular cases wherever they occur," Champagne told The House.

Carleton University professor Stephanie Carvin sees the dispute as a red flag for Canadian officials.

"It is emblematic of the kinds of techniques that China might use in order to retaliate against a ... decision that it didn't like," Carvin said in an interview with CBC News.

In June 2017, before the case went into a closed-door trial, China's ambassador to Canada told CTV News that the case shouldn't be "politicized" and should be allowed to unfold in court.

Last year, shortly after Trudeau's first prime ministerial trip to China, authorities there released another Canadian who had been held for two years.

Kevin Garratt had been arrested in 2014 on suspicion of stealing state secrets and spying.

Garratt and his family adamantly denied any wrongdoing, and both the previous Conservative government and the Liberal government advocated on Garratt's behalf at the highest levels.

Push to ramp up trade talks

Despite these concerns, Ottawa is being pressured to deepen ties with Beijing, and quickly.

Canada's former ambassador to China, Guy Saint-Jacques, said conditions are "ripe" to negotiate a trade deal, and predicts the complicated talks could be completed in three years.

Justin Trudeau met with Chinese President Xi Jinping in 2016 before the G20 Summit in Hangzhou, China. On Saturday, Trudeau will head to Beijing to see if he can strengthen trade relations with China. (AFP/Getty Images)

"If we don't go ahead, I think that China will feel, again, that we have left them at the altar, waiting," Saint-Jacques said in an interview with Radio-Canada.

Government sources tell CBC News that during the four rounds of exploratory trade talks, Chinese officials made it abundantly clear they want a free trade agreement with Canada.

The sources said the Chinese are eager to access Canadian natural resources, clean technologies, agriculture and e-commerce systems.

Canadian business leaders have called for talks to take place, in the hopes of one day selling goods and services to China's growing middle class of about 600 million people.

"They will turn to others... we are not the only game in town," Saint-Jacques said.

Former Quebec premier Jean Charest agreed, saying Canada should "aggressively" pursue an agreement.

Charest helped the former Conservative government launch free trade talks with Europe, and has extensive business dealings in China.

"No one gets up in the morning and asks themselves 'why don't I do a deal with Canada today?' It doesn't happen that way. We are the ones that have to go out there and hustle for it," Charest said in an interview.

"We are 36 million people with a high standard of living. If we don't trade, we are not going to be able to maintain the lifestyle we have here," he said.