Chretien's pollster, Michael Marzolini, has been crusading for this idea for years, and I presume he's got some polling number to back him up on it. While I don't really think it's a good idea for the government to kiss away such a large source of revenue, but it's hard to see how this wouldn't be a winning strategy politically. Everyone hates the GST, it would counter the Solberg budget, and it would remind people of Martin's flip-flop on the GST way back when (not that anyone really cares about that in my opinion...). Plus, it would be the kind of constructive policy the Tories could hold up as proof that they're not just campaigning against corruption.
On the flip side, it could make balancing the books very difficult if they do win, but I suspect that's a problem the Conservatives wouldn't mind finding themselves with, after twelve years in opposition.