"Why is the Ontario Gov't sitting on it?"
A better question is - Have they got it?
Let's not assume that it has been completed. Even if completed, has Ontario paid for it? If not then they can not release it.

There is also the question, if they paid for it and have it do they agree with it?
They may not agree entirely with it or some aspect of the desired recomendations in the report needs to be completed before release.

For instance some native communities need to be on board and some foot dragging, or compromise has to be reached with them, otherwise Ontario government could end up with egg on their face.
Remember this government wants to do things 'Right' and not make a mistake. ;-)