Steven Harper is pushing hard to call a snap election in the next week or so. Canadian election law mandates a 6 week campaign, so we'd actually be at the polls no earlier than mid-October.
Why is Harper so keen on an election right now? The political landscape isn't really in his favour; the best he could hope for would be another Conservative minority government. That's not in his personal best interest, as it would likely result in his position being reassessed by the party.
Harper claims that the current parliament is dysfunctional, but that clearly isn't the case. By any objective measurement, this parliament has been extremely compliant in its minority status. The Conservatives have gotten quite a bit of their agenda through, which is unusual in a minority parliament, especially considering that they have no real allies in the other parties.
Dion has suggested that Harper wants to preempt several by-elections that have been called, and that he wants to avoid committee hearings on Conservative scandals. I don't think that's really it. Yes, the Liberals would get a bit of momentum from wins in the by-elections, but that's not certain and hardly fatal anyway. The committee hearings are important, but they haven't gotten much traction in the public view.
In my view, Harper is terrified of Obama. Improved relations with the US was the primary selling point the Conservatives used in the last election and that would be squarely on the Liberal's side with Obama in the Whitehouse. Further, it'd be seen as inappropriate for the Liberals to assume that Obama will be the president before he's elected, so Harper is desperate to get Canadians to the polls before November 4th.