An Air Inuit de Havilland Dash 8-300, registration C-GIAB performing flight 3H-802 from Montreal,QC to Kuujjuarapik,QC (Canada) with 9 passengers and 3 crew, was enroute at FL250 about 160nm north of Montreal when the crew received a cabin pressure warning light with the cabin altitude above 10,000 feet and initiated an emergency descent to 14000 feet. At 14000 feet the cabin altitude stabilized at 7000 feet. The crew decided to return to Montreal where the aircraft landed safely about 2 hours after departure.