The NDP has always been willing to cooperate with the Liberals. The Liberals would rather eat broken glass than make any kind of deal with the NDP - and forget about PR - the Liberals will never go for it because it would impede their chances of regaining a majority gvernment and being Ontario's natural party of government again.
Most likely scenario after next Ontario election is that the PCs come in first, fall short of a majority...and the Liberals will prop up a Hudak minority government rather than cooperate with the NDP.