According to this Globe and Mail article, both Dalton McGuinty and Tim Hudak have ruled out coalition governments and would I assume try and govern during the recent federal period of minority governments with Paul Martin and Stephen Harper.
Hudak is obviously a no brainer to go against teaming up with NDP, but things are a little more nuanced with McGuinty. Saying he would partner before the election wouldn't help. It would scare away right leaning liberals that wouldn't want anything to do with the NDP having a portion of power. Those worried about public sector salary increases would also vote against NDP involvement in government, but really they wouldn't vote Liberal given McGuinty's record during the past eight years.
Of course once the election is over and assuming a minority situation, McGuinty could easily try for a coalition if he has less seats than Hudak. What would be interesting is public perception. If he has one seat less, not really a huge deal, but double digit seats less might prove unpalatable to the public.
In terms of the NDP, a coalition with the Liberals and getting a piece of government would be a short term game. However I would guess like their federal cousins, the NDP is looking to supplant the Liberals in Ontario and wouldn't have huge interest in propping up a regime that is past its due date. Whatever happens, things will be interesting, with a lot of histrionics.