After more than two and a half years of diplomatic squabbling, Canada and China saw their relations sink to a new low this week after two Canadian citizens were handed stiff sentences by Chinese courts -- one of them a death sentence.

Ottawa says the two men and a third citizen have been the victims of tit-for-tat punishments meted out after a top executive for Chinese tech giant Huawei was arrested in Canada in December 2018 on a US extradition warrant.

Experts say only US intervention will break the "impasse." Here is a look at the saga and what could happen next: 

- The arrest that started it all - 

Meng Wanzhou, the 49-year-old daughter of Huawei founder and CEO Ren Zhengfei, was arrested during a stopover at the Vancouver airport on December 1, 2018 at the request of the United States, where she is wanted for fraud.

For Roromme Chantal, a political science professor and China specialist at the University of Moncton in New Brunswick, that detention "suddenly poisoned relations which had been very good between the two countries since the 1970s."

Meng, the company's chief financial officer, is accused of defrauding HSBC by falsely misrepresenting links between Huawei and Skycom, a subsidiary that sold telecoms equipment to Iran, putting the bank at risk of violating US sanctions against Tehran as it continued to clear US dollar transactions for Huawei.

Both Meng and Huawei deny the accusations, and the government in Beijing says the case is being used by the United States to weaken the Chinese company, the world's largest supplier of telecom networking gear.

"In this affair, Canada is clearly being held hostage in a geopolitical rivalry between the United States and China," said Chantal, who believes that China will do "everything to obtain the release of Meng Wanzhou."

Final arguments in Meng's extradition trial started Wednesday in Vancouver. During the entire legal battle, she has lived in her mansion in the western coastal city, wearing an ankle monitoring bracelet at all times.

The hearing is scheduled to wrap on August 20, but a decision in her case is not expected for several months -- and appeals could make that longer.

 - Chinese 'reprisals' - 

Just days after Meng's arrest, China detained two Canadians -- businessman Michael Spavor and former diplomat Michael Kovrig.

Both were tried and convicted in March this year of espionage -- charges that Canadian Prime Minister Justin Trudeau has said were "trumped up."

On Wednesday, a Chinese court sentenced Spavor to 11 years in prison. 

And the day before, a third Canadian, Robert Lloyd Schellenberg, saw his death sentence on a drug smuggling charge upheld.

"The timing is not accidental. There is no coincidence," said Guy Saint-Jacques, a former Canadian ambassador to China who has called the arrests tantamount to "hostage-taking."

"The Chinese want to put pressure on Canada and we can clearly see the Chinese strategy at work with the increasing severity of its moves. It is a strategy increasingly used by China and a real concern for democracies," he told AFP.

Canadian Prime Minister Justin Trudeau condemned Spavor's conviction and sentence as "unacceptable and unjust." Many of Canada's allies expressed solidarity with Ottawa.

Despite the support, "there is a remarkable and growing asymmetrical power imbalance between Ottawa and Beijing" that limits Canada's ability to maneuver," said Gordon Houlden, director of the China Institute at the University of Alberta.

- How to resolve the crisis? - 

For Chantal, there is only one way out: "trilateral diplomacy" with the United States and China.

"It is difficult to envisage any concessions from China without the release of Meng Wanzhou," he said, adding that if she is not set free, China will continue "to weaponize the justice system."

Kovrig is still awaiting sentence, but no date has been announced.

Saint-Jacques said he expected Kovrig to be handed "an even more severe sentence because the Chinese know that this will have a strong impact since he is a former diplomat."

US Secretary of State Antony Blinken on Wednesday called on Beijing to immediately release Spavor and Kovrig, while Canadian Foreign Minister Marc Garneau said "intense discussions" with Washington on securing their release were under way.

"One of the solutions would be for the United States to drop the charges against Meng or make a deal with China," Saint-Jacques said, while adding: "But so far, the US doesn't seem ready to budge."

Houlden said he did not think the United States "has the same sense of urgency that is felt in Canada" about the matter.

Meanwhile, calls are growing in Canada to put pressure on Beijing by threatening to boycott the upcoming Winter Olympics in the Chinese capital.