Arusha police Cmdr. Liberatus Sabas told the Toronto Star that Susan Wells, 41, of Collingwood, ON was shot in the head. But he also told the CBC she was slain with a machete.
The suspect arrested in her death is reportedly Joseph Kimaro, a youth with whom Wells worked as an overseas volunteer.
Former Collingwood mayor Terry Geddes knew Wells through the congregation at the local United Church.
"She was a young person who carried on the proud tradition of service to the community set by her parents," said Geddes.
Wells had been working with young people in Tanzania for the last several years, holding fundraisers through her church.
The Department of Foreign Affairs would not release further details.
- With files from Ian Adams