EKOS conducted a poll between March 27 and April 3, just as the new gas plant allegations were made, and found the Liberals ahead with 32%, with the New Democrats in second at 29% and the Progressive Conservatives in third with 27%.
Forum conducted a poll more recently, on April 7, and found the Tories surging ahead with 38% to 31% for the Liberals and just 23% for the New Democrats.
Skeptics note: EKOS and Forum just had very good showings in the Quebec election. Pick your poison, then.
In pre-scandal polling, the Liberals had around 36%, the Tories around 33%, and the NDP around 25%. According to EKOS, both the Liberals and Tories have since faltered to the benefit of the NDP. According to Forum, the PCs surged to the detriment of the Liberals. That would seem to make the most intuitive sense, but Ontario has been impossible to gauge for some time now.
The sum of all of this is that the aggregate puts the Liberals and Tories neck-and-neck with 33% apiece, and the NDP up slightly to 26%. It remains a very close race in Ontario.
With these aggregate levels of support, the Liberals would likely be able to win another minority government of 43 seats, with 38 seats going to the Tories and 26 seats going to the NDP.
The methodology used to weigh polls can be found here. By including polls in the average, no representation as to the accuracy or equivalency of the methods used is implied, nor should inclusion be seen as an acceptance, endorsement or legitimization of their results. The weighting scheme takes this partly into account. See here for a complete rundown of the latest polls in Ontario (external link).
The chart below shows the evolution of the weighted polling averages since July 2013 (note that the date listed is the final field date of the polling included in the aggregation at the time of the update).