It’s kind of funny, Americans are blaming Canadians (article):
Mr. Pataki said the current theory that state officials were pursuing is that there was a surge of power somewhere in Western Ontario that triggered the domino-like cascade of power plants’ shutting down.
And the Canadians are blaming the Americans (article):
The Prime Minister’s Office first said lightning had struck a power plant in the Niagara Region on the U.S. side of the border, but subsequently said there had been a fire at a Con Edison power plant in Niagara Falls, N.Y.
I’ve heard that it was an explosion in Manhattan, lightning strikes in Niagara, nuclear plants in Pennsylvania, somewhere in southern Ontario. Who knows.
Update: Turns out it was the Americans.