On touchdown at Norway House (YNE), when propeller reverse was selected, the Metro II aircraft turned toward the left side of runway 05. Before the turn could be corrected, the left main tire passed beyond the runway lights and contacted loose snow. The aircraft traversed a ditch then climbed a soil-covered rocky embankment. All three landing gears collapsed and the aircraft came to rest upright and on its belly. The crew and passengers exited the aircraft via the over-wing exits and the main door stairway. FINDINGS AS TO CAUSES AND CONTRIBUTING FACTORS: 1. The left engine fuel control support assembly failed in fatigue and released one of three attachment bolts, which resulted in a slight displacement of the fuel control and changed the propeller control dimension. As a result, Beta pressure was achieved and propeller reverse was available for the left engine before it was available for the right engine. 2. The pilot selected thrust reverse without confirmation that the Beta lights were on for both engines, and the aircraft veered from the runway, most likely as a result of temporary asymmetric thrust.