China's foreign ministry spokeswoman, Hua Chunying, identified the third Canadian as Sarah McIver, who was serving "administrative punishment" due to "illegal employment".
This latest detention comes after Meng Wanzhou, chief financial officer of tech giant Huawei, was arrested in Vancouver on December 1 at the request of the USA, where she is wanted on fraud allegations.
Though Meng has been granted bail, she faces possible extradition to the USA for allegedly doing business with Iran in violation of USA sanctions.
She was taken into custody at the request of the USA government and is free on CAN$10 million bail while awaiting an extradition hearing.
Hua referred further questions on McIver to the ministry of public security.
"There are tens of thousands of Canadians that live, travel and work in China", Trudeau said at a year-end news conference.
President Donald Trump told Reuters last week that he would personally intervene in the Meng case if it would benefit USA national security or help close a trade deal with China. Until her detention, he said, she hadn't had any problems with her visa.
The official Canadian government position as of Wednesday was there was no reason to assume the arrest is connected to the detention of two other Canadians.
An Alberta woman has been detained in China, but federal officials do not believe there's any connection to the previous two detainments.
"We're going to continue to defend (the Canadians who were detained), to stand up for them, to ask for more information on the charges being brought forward, or the reasons for detention, and we will continue to engage on a case-by-case basis in a thoughtful way on any consular cases that come up", Trudeau said.
"In China there are no coincidences". Incidentally, Wanzhou's arrest took place on the same day that US President Donald Trump and Xi Jinping (the president of China) met in Buenos Aires and agreed to a trade ceasefire for 90 days during which time, both parties would negotiate.
Kovrig served as a diplomat in China until 2016 and has been working for the International Crisis Group, a non-governmental agency focused on ending conflicts.
Canada's Global Affairs office stated that they had acknowledged the detention, however, didn't make further announcement on the incident nor the links to Meng's arrest.
She is the also vice chairman of Huawei, the second-largest smartphone creator in the world and the daughter of the company's founder, Ren Zhengfei.