OTTAWA—Canada on Friday called for the immediate release of two citizens detained in China in the aftermath of the arrest in Vancouver of a Huawei Technologies Co. executive, sharpening its tone after walking a cautious line with Beijing.

In a statement, Canadian Foreign Minister Chrystia Freeland said she was “deeply concerned by the arbitrary detention” last week of former diplomat Michael Kovrig and entrepreneur Michael Spavor. She said Canada “[called] for their immediate release.”

Canadian...