RCMP say the crash occurred early Sunday evening in the Skagit Bluffs area, about 32 kilometres east of Hope.
Investigators believe the man's westbound pickup truck hit the gravel shoulder of the highway and the victim lost control of the 2002 Ford F150 as he tried to steer back onto the pavement.
The truck veered across Highway 3 and down an embankment, hitting two trees and landing, partially submerged, in the Skagit River.
The man died at the scene but a 21-year-old woman passenger was treated in hospital for minor injuries.
RCMP believe weather and road conditions did not contribute to the crash, but driver inattention, mechanical problems, speed or alcohol have not been ruled out.