OTTAWA - Prime Minister Justin Trudeau is on his way to a major international summit in Japan, hoping to make progress - or at least find allies - in Canada's multi-front dispute with China.

The G20 leaders' summit in Osaka comes at a critical moment for Trudeau, with a fall election in the offing and Canada having had no luck so far in its efforts to secure the release of two Canadians in China's custody - Michael Kovrig and Michael Spavor.

China detained the pair, a former diplomat and an entrepreneur, days after Canada arrested Chinese high-tech executive Meng Wanzhou in December on a U.S. extradition warrant. They've been arrested on allegations of undermining China's national security.

As Trudeau set out for Osaka, the two countries dug in. In a regular daily news conference at China's foreign ministry in Beijing, spokesman Geng Shuang again pressured Canada to free Meng, who is currently out on bail in Vancouver, awaiting an extradition proceeding that could last years.

“Our position is very clear,” said Geng. “We urge the Canadian side to take our solemn concerns seriously, immediately release Ms. Meng Wanzhou and ensure that she returns to China safe and sound.”

Canada, for its part, insists it is merely following the rule of law.

“There has been no political interference in this case,” said Adam Austen, a spokesman for Foreign Affairs Minister Chrystia Freeland. “It has been entirely about officials taking decisions according to Canada's commitments.”

On Tuesday, China appeared to up the ante, seeking to suspend imports of Canadian meat on the grounds that its authorities don't trust Canadian assurances about the quality of its exports. China has previously obstructed shipments of Canadian canola, peas and soybeans.

Canadian ministers and officials have had little luck getting to speak to their opposite numbers in China about any of it. International Trade Minister Jim Carr said Wednesday he's not concerned about damage to Canada's brand at this point.

“Someone is going to have to come up with some proof that there's something wrong with the product and that the product originates from Canada,” Carr said following a speech in Toronto. “We don't know where the product originated so there are unanswered questions here and (we will) seek to answer them quickly.”

A government spokesperson confirmed that the government has called in the RCMP and the Canada Border Services Agency to investigate an inauthentic certificate.

Quebec Premier Francois Legault, whose province generates about 40 per cent of Canada's pork, called Beijing's latest move “draconian” and urged the federal government to come up with help for hog farmers. He also left the door open to possible retaliatory measures.

“Trade has to be fair, it has to be possible in both directions,” Legault said. “At this time, we can't rule anything out.”

To get a message across in Osaka, Trudeau will lean on the power and influence of the mercurial Donald Trump, who has committed to raising the issue of the two detained Canadians when the U.S. president meets one-on-one with China's president Xi Jinping. A Canadian government official says Canada is “unlikely” to request such a meeting of its own.

The G20 includes countries with large economies from all over the world, with much more divergent interests than the smaller G7. Its members include Russia, China, Turkey, Indonesia, Brazil and South Korea.

During last week's meeting with Trudeau in the Oval Office, Trump pledged his support for Canada's detainees in China and committed to raising the issue with Xi. “Anything I can do to help Canada, I will be doing,” he said.

It should come as no surprise that China doesn't want to entertain a meeting with the prime minister, which is why Trump remains Canada's best hope, said David Mulroney, a former Canadian ambassador to China.

“That would be the strongest card that could be played in our interests,” he said. “It would be an American card played to say ... 'If you want a normal relationship with us, you'll leave our allies alone.”'

Currying favour with other leaders who face similar challenges from China would also be helpful, Mulroney added.

“If we can build this sense of shared purpose in pushing back against China, in not allowing ourselves to be isolated like this, that's a big step forward,” he said.

“It is in America's interest and it is in the interest of a lot of other countries to see China pull back from hostage diplomacy and bullying ... The only way to counter that is through collective action and that is a long, hard slog.”

Canada doesn't play offence very much, but should make an exception in this case and talk to other leaders about the detained Canadians, said Christopher Sands, the director of the Center for Canadian Studies at John Hopkins University.

Beyond asking for Trump's support, countries like Japan, South Korea and perhaps India might be willing to do the same, helping to strengthen the U.S. president's commitment to the cause, Sands said.

An official confirmed Trudeau is expected to sit down with South Korean President Moon Jae-in at the summit - a conversation where the detentions are likely to be raised.

To date, a list of countries including Australia, France, German, Spain, the U.S. and the U.K. have spoken in support of the detained Canadians.

Rohinton Medhora, the president of the Centre for International Governance Innovation, said he will be watching to see who else Xi meets in bilateral one-on-one sessions. The G20 is an opportunity to showcase Canada as a major diplomatic player - particularly with Canadians poised to go to the polls in October, he said.

“I would say the pressure (is on), especially going into an election when you have to demonstrate that Canada is better and different than four years ago.”

Conservative foreign-affairs critic Erin O'Toole echoed that point, saying it is critical Canada not let the opportunity afforded by the G20 pass, especially given the upcoming election campaign.

“As of September, the writ will drop,” he said. “This is really the last major time to really shake up and try to stop the spiral of the China relationship.”