VANCOUVER, British Columbia — Canadian police said they arrested three suspects Friday in the slaying of a Sikh separatist leader last June that became the center of a diplomatic spat with India, and are investigating possible ties between the detainees and the Indian government.

Three Indian nationals in their 20s identified as Kamalpreet Singh, Karan Brar and Karampreet Singh were arrested in Edmonton, Alberta on Friday morning in the slaying of 45-year-old Hardeep Singh Nijjar by masked…