The "best thing" U.S. President Donald Trump could do to secure the release of Canadians detained in China is to abandon Washington's push to extradite Huawei executive Meng Wanzhou, Canada's former ambassador to China said today.

John McCallum — who was fired from the high-profile diplomatic post by Prime Minister Justin Trudeau in January after he waded into Meng's extradition case in front of Chinese-language journalists — told CBC News from Beijing that the prime minister's options for repairing Canada's diplomatic relationship with China are limited as he prepares for this weekend's G20 summit in Osaka.

"I don't think there's an easy, immediate fix at this point," McCallum said, adding that Trudeau's best hope for securing the release of Canadians Michael Kovrig and Michael Spavor from Chinese custody might lie with the mercurial President Trump.

"I certainly hope that (Trump) can help. I think from the point of view of restoring relations and releasing our hostages, the best thing that Trump could do would be to say that he is no longer seeking to extradite Meng Wanzhou," McCallum said.

"Now, I doubt that he will say that. He could ask Xi to release our hostages. I don't know what Mr. Trump is going to do. He's a difficult person to predict."

Meng Wanzhou arrives at her home after attending court in Vancouver on Wednesday, May 8, 2019. (Ben Nelms/CBC)

President Trump is expected to meet with Chinese President Xi Jinping on the sidelines of the G20 summit to try to hash out a solution to the burgeoning trade war between the two countries. He may also raise the topic of the two Canadian detainees; during a meeting with Trudeau at the White House last week, Trump said that he would do "anything" he could to help secure their release.

Another former Canadian ambassador to China, David Mulroney, told CBC news that he's surprised to hear McCallum still weighing in on this subject, given the circumstances of his departure from the job.

"My own sense (is) if I had gone through what he has gone through ... I would refrain from making public comments," Mulroney said, adding that McCallum's speculations about Meng's extradition case weaken Canada's bargaining position.

"The unfortunate reality is that while senior people make comments like this, it reinforces for the Chinese that the Canadians are going to crack."

Canada's diplomatic relations with China have been on thin ice since Meng, the 47-year-old chief financial officer for Chinese telecommunications giant Huawei, was arrested at Vancouver International Airport in December, 2018 on a stopover from Hong Kong to Buenos Aires.

According to an indictment unsealed in January, Meng and Huawei face 13 criminal counts of conspiracy, fraud and obstruction in the U.S. The charges relate to an alleged scheme to circumvent sanctions against Iran through a shadow company in Tehran that prosecutors say was actually controlled by Huawei.

Since Meng's arrest, Beijing has put heavy pressure on Canadian exporters, blocking shipments of canola seed and pork. It also arrested Spavor and Kovrig and accused them of espionage.

Michael Spavor, left, and former Canadian diplomat Michael Kovrig, right, have been accused of espionage by the Chinese. (The Associated Press/International Crisis Group/The Canadian Press)

The Trudeau government's own efforts to open a dialogue with Beijing on the detainees have stalled. Earlier this month, CBC News reported that Beijing snubbed Trudeau's personal request for a conversation with Chinese Premier Li Keqiang about the detainees.

Trudeau requested the phone call with Li prior to a sentencing hearing for Robert Schellenberg, a Canadian man accused of drug smuggling in China. China ignored and ultimately rejected the request; a Chinese court subsequently sentenced Schellenberg to death in a sudden retrial.

"The Chinese leadership has not wanted to speak to us. Ideally, it would be better if our people could speak to their people," McCallum said.

This week, Meng's lawyers issued a statement saying it would be in "Canada's national interests" to drop the extradition proceedings.

"That's what China wants and China has been very clear in stating that," McCallum said. "I'm not suggesting Mr. Trump will do that, but if he did, that would certainly be a huge help."

This isn't the first time McCallum has speculated publicly about Washington withdrawing its extradition case. Shortly before Trudeau asked for his resignation in January, McCallum was quoted telling a gathering of Chinese-language journalists in Toronto that he thought Meng had a strong case to fight extradition to the U.S., and listed several arguments he thought could help her with her case.

Days later, McCallum said he misspoke with those statements. A day after that, he told a StarMetro Vancouver reporter it would be "great for Canada" if the United States dropped its extradition request.

McCallum is in Beijing in his new job as senior strategic adviser for the Toronto-based law firm McMillan LLP, advising Canadian and Chinese businesspeople on navigating the fraught relationship between the two countries.

"There's a great concern," he said. "The state of relations between Canada and China is at a low point. And so, my purpose is to talk to companies to see how things are going, perhaps help them or advise them under the circumstances."

McCallum said he spoke with his former colleagues at the Canadian embassy on Monday to get an update on Spavor and Kovrig. He said embassy staff continue to visit the two men more than once a month.

"I am told they are holding up as well as one might expect. But obviously they would like a quick resolution and they would like to be released," he said.

McCallum said he doesn't think "it is the end of the world" that Canada hasn't filled his old job yet, adding that the current head of mission in Beijing, Jim Nickel, is helping to fill the gap.

"Whether or not we have an ambassador on site is not going to be the decisive factor."