Simeon Garratt said his parents were out for dinner with friends in the Chinese city of Dandong, near the border with North Korea, when they were detained Monday night.
"As of right now my parents are being held in an undisclosed location. I have heard that they're safe but they're just a bit confused. They actually have no idea what's going on," the 27-year-old said in an interview from Vancouver.
Garratt said his younger brother, who lives in Dandong, was told of his parents' detention by Chinese authorities and instructed to bring spare clothes and toiletries for them, but wasn't allowed to speak with the couple.
"He was brought in for questioning and that was relayed to him by them. He didn't get to talk to them. (Officials) said maybe later," Garratt said.
China's official Xinhua News Agency has reported that Kevin Garratt and Julia Dawn Garratt are being investigated by the state security bureau on suspicion of stealing state secrets about China's military and national defence research.
Simeon Garratt said his parents have lived in China for the past 30 years and called their detention extremely confusing.
"At this point it just seems like my parents are getting caught up in something that's a whole lot bigger than them," he said.
"My parents basically run a coffee shop, my mum taught some courses at the university there, and they've done some human aid work in North Korea, but nothing ever detrimental or negative towards China, or anything like that."
A spokesman for the department of Foreign Affairs said Canadian officials are in contact with local Chinese authorities and are providing assistance to the detained couple.
Garratt added that government officials had told him a Canadian consular official in Dandong was expected to be able to meet with his parents on Wednesday.