There is no chance whatsoever that the NDP is going to overtake the Liberals this time around.
If the NDP is going to replace the Liberals as the official opposition in the near future, one thing has to happen this election. Harper has to be held to a minority. Otherwise, the Liberals will have 5 years to recover and any momentum the NDP might have in Quebec will be lost. Hold a Harper to minority and the Layton will be able to proclaim himself as the only true opposition to Stephen Harper as both the Liberals and Bloc continually prop up the government as they search for new leaders,