Harper's Québec gambit is quite brilliant when you think of it. It gives him the opportunity to wreck opportunities for both the NDP & Liberals in Quebec and take them both down with one blow.
Increasing Conservative support in Quebec blocks Liberal growth opportunties in some parts of the province (and thereby reduces the potential National total for the Liberals) and takes away exisiting NDP seats in Quebec City & some of the regions (thereby reducing the National total for the NDP). Meanwhile, the National seat total increases for the Conservatives and brings them closer to Majority Range again. Quebec gains would allow Harper to make up for any losses in the Maritimes and Ontario.