Ontario Provincial Police responded to a vehicle collision on Highway 403 heading west on Highway 6 South around 11 a.m.
The vehicle appears to have overturned in a ditch.
A 74-year-old man from Bradford was found dead at the scene, police said.
Investigators are examining the possibility of a medical incident that caused the crash.
The ramp to Highway 6 South is expected to remain closed for several hours as police conduct an investigation.
