Canada's foreign ministry says it is trying to make contact with a second Canadian who is believed to have been detained in China.
Michael Spavor, a businessman based in Dandong near the North Korean border, had contacted Canadian officials this week to say he was being questioned.
Foreign ministry spokesman Guillaume Bérubé said Canada was working hard to determine Mr Spavor's whereabouts.
It comes after former diplomat Michael Kovrig was arrested in China this week.
Canadian officials say the reason for Mr Kovrig's detention remains unclear
But Chinese state media have reported that Mr Kovrig is being held "on suspicion of engaging in activities that harm China's state security".
Mr Kovrig currently works for think thank the International Crisis Group (ICG), who have said they are concerned for his health and safety.
At a news conference in Ottawa on Wednesday, Foreign Minister Chrystia Freeland said Mr Kovrig's case had been raised directly with Chinese officials.
She also said a second Canadian had contacted them earlier in the week because "he was being asked questions by Chinese authorities".
She did not name the individual, saying it was "delicate situation" and she wanted to respect his privacy.
But Mr Bérubé later named the man in a statement as Mr Spavor and said he was "presently missing in China".
Mr Spavor runs an organisation called Paektu Cultural Exchange, which organises business, culture and tourism trips to North Korea.
He is a regular visitor to North Korea and was a well known commenter on Korean issues. His last tweet, on Sunday, said he was about to travel to Seoul in South Korea, but he did not arrive on Monday as planned.
The detentions have come after Canada arrested Chinese telecoms executive Meng Wanzhou last week.
Ms Meng is the chief financial officer of Huawei, one of China's biggest telecoms companies, and the daughter of its founder.
She was arrested at the request of the US and is accused of violating sanctions on Iran. She was granted bail on Tuesday for C$10m (£6m; $7.4m) bail but could be extradited to the US.
China has demanded that Canada release Ms Meng, and has threatened unspecific consequences.
Canada has said there is currently no "explicit indication" of any link between her arrest and Mr Kovrig's detention.