Mr. Spavor gained prominence for helping arrange the visits to North Korea by Dennis Rodman, the former N.B.A. star. During one of those visits, Mr. Spavor met the country’s reclusive leader, Kim Jong-un, and in appearances in Beijing he would fondly speak about their friendship, though the extent of it was not clear.

He posted notes on Twitter and Facebook on Sunday that he planned to travel to South Korea on Monday for several days of consulting work. But he did not appear, as planned, at a lecture organized there by the Royal Asiatic Society, according to members of the group.

Chrystia Freeland, Canada’s foreign minister, disclosed the second case, and during a news conference in Ottawa on Wednesday she urged China to let the legal process unfold. She also warned the administration of President Trump not to further politicize what started as a legal matter involving accusations that Huawei had committed bank fraud.

Mr. Spavor was detained on Monday by state security officials in Liaoning, the province along the border with North Korea where he has lived, a spokesman for the Ministry of Foreign Affairs, Lu Kang, said on Thursday. That same evening officials in Beijing arrested Michael Kovrig, a former Canadian diplomat who since last year had worked for the International Crisis Group, a nongovernmental research organization that seeks to defuse international conflicts.

Image Michael Spavor Credit... Associated Press

On Wednesday, the same spokesman suggested that Mr. Kovrig worked for an organization that had not been legally registered under a new law, but the latest statements suggested he faced far more serious criminal charges, complicating efforts to win his release, or Mr. Spavor’s.