By John Deverell Nobody plays divide-and-conquer more relentlessly than Stephen Harper. The PM this week is selling himself as “Captain Canada,” the only guy to squelch a Quebec separatist revival. This is the same Stephen Harper who, not long ago, was urging Albertans to build a firewall between Tar Sands Central and the rest of Canada. Then he was “Captain Conflict.” His current game, not so…