Ontario Provincial Police said the plane went down around 4 p.m. Friday on Chappie Lake, south of Kenora.
Police said search and rescue teams found the plane.
Two of its occupants were dead.
A third was seriously injured but succumbed to her injuries in spite of efforts to save her.
OPP said the victims have been identified as 41-year-old Nikolas Rajala, 40-year-old Teresa Rajala, and 36-year-old Lynn Bohanon, of Grand Rapids, Minn.
Police said they were staying at an area fishing lodge and were planning to fish on Chappie Lake Friday.
The cause of the crash is under investigation.