There are only 2 ways Harper continues to be Prime Minister after the election:
1) His party gets 35% of the vote and the NDP/Liberals split so perfectly that the CPC ekes out an incredibly slim minority.
2) He has a strong minority and the Block holds the balance of power, not the Liberals or Greens. If that is the case, then it would be hard for the Liberals and NDP to try to form a coalition because they'd also need the backing of the Bloc, and that is what tanked the 2008 attempted coalition.
But in scenario 2, the Bloc would vote against the PCC anyway. They always do. Unless they'd want to sabotage the whole thing, which wouldn't fly in Quebec. So does it matter if the Bloc is officially part of the coalition or not?
Anyway, I almost want a PCC minority just to see how things would unfold. It'd be fascinating to watch. I also think we'd see better cooperation between the Liberals and the NDP in that scenario than if one or the other wins a minority.