While not always a perfect indicator, one thing I find that helps determine election results is candidates. Much like comparing the number of lawn signs, I find comparing the speed which a party reaches a full-slate to help determine it's level of support in the coming election.
At the time of the writing, the parties have the following number of candidates:
NDP - 42
PC - 29*
Lib - 28
Grn - 15*
more to come.
* = from Wikipedia, as their website has yet to list the number.