If you recall, AIG Inc. was one of the companies that received bail out money from the US government during the height of the credit crunch. The Canadian subsidiary was not impacted directly during this time except for the possible bad PR associated with the name.
I believe that this will bode well for the future of consumers now that the second largest mortgage insurer in Canada is backed by such a strong investor. This should ensure continued competition in the mortgage insurance market that continues to be dominated by CMHC.
You can view the press release and learn more about both AIG United Guaranty Mortgage Insurance Company Canada and the Ontario Pension Plan Press release.