We have the same reserves as Manitoba and Quebec, topography is much the same. The issue is the governments unwillingness to negotiate for the use of the land that needs to be used for building dams, how remote these projects will be and also their unwillingness to tell the environmentalists to fuckoff, because they will lose votes. Quebec did this back in the 70's with the James Bay project. I haven't heard anything about the environmental impact of this project now.
Manitoba took the same stance and built projects in their north, the Nelson River Project and the Churchill Diversion, both in remote areas and topography that isn't dissimilar to what you would find in northern Ontario.
Sorry Dirk, but this is not quite right.
The complete potential for hydroelectric development in Ontario was well known by the 1940's, including all of the northern reaches of the province. Those sites were developed starting as early as the 1920's and continued though to the 1960's, long before Quebec's development of James Bay and Manitoba's development on the Nelson River. In those days, Ontario Hydro pretty much did what they wanted since there were no environmentalists to tell fuck off to, and indigenous peoples were just fucked over, no matter what they said. (decades later, apologies were made, e.g.
http://www.cbc.ca/news/canada/thunder-bay/gull-bay-first-nation-gets-apology-from-ontario-power-generation-1.2870505.
Another example was the deliberate flooding of several towns along the St. Lawrence for the Saunders/Moses power project.
http://www.thecanadianencyclopedia.ca/en/article/the-lost-villages/.
So Ontario Hydro certainly had the cajones to fuck whomever over in the name of progress. By the end of the 1960's, every major site worth developing for hydroelectric power in Ontario had been tapped. This is why Ontario Hydro started to build coal fired stations beginning in the 1950's. Growth in electricity demand could no longer be met by hydroelectric development in Ontario.
Now, there are a few major rivers in northern Ontario without any hydro development .... the Albany, the Severn, the Attawapiskat, the Winisk. But the topography along these rivers is not the same as the sites where the big developments are located on the Nelson River in Manitoba and the Eastmain and Grande Rivers in Quebec. The rivers in northern Ontario have large flows, but virtually no drop in elevation (not enough "head") and no sites at which to build a dam and a forebay. Not enough head and nobody's happy.
In summary, the hydroelectric resources are not the same, with installed hydroelectric capacity is as follows:
Ontario - 8,400 MW
Quebec - 36,000 MW
Manitoba - 5,200 MW.