Kimberly Ann Kalinowski, 22, of Livonia, Michigan, and the teenager, whom police did not name, headed north last week after the boy apparently had a fight with his mother, Michigan police said, according to the Canadian Press.
Ms Kalinowski made a phone call from Toledo, Ohio, earlier in the week, but there was no sign of the two until they were seen near Dryden, Dryden police constable Geoff Hartley said.
Police chased a car after getting an armed robbery complaint from a hotel in Wabigoon, south of Dryden. The high-speed chase ended when the car ran into a lamp-post.
Once police reached the car, they found that Ms Kalinowski and the teenager had both been shot in the head.
An autopsy showed that Ms Kalinowski, who was driving, died instantly. The teenager died shortly after the crash in a hospital.
Mr Hartley said it appeared the boy shot Ms Kalinowski before turning the gun on himself. A .22-calibre handgun was found in the vehicle, he said.
Michigan police had issued an arrest warrant for the youth on charges he had abducted the sitter.