The Mississauga City Hall website news release http://www.mississauga.ca/portal/cityhall/pressreleases?paf_gear_id=9700020&itemId=102600359n&returnUrl=%2Fportal%2Fcityhall%2Fpressreleases
identifies the cost premium for the Green Energy at $30 per megawatt-hour (MWh -- not kWh in the press variant cited by Jerry). That's a premium of "only" $0.03 per kWh. This almost seems like a great deal, except the availability of Green Energy is limited. It seems as if the customer is paying the premium on the majority -- conventional power from the grid to provide the extra margin to cover the cost of the Green version.
If the windmills, solar cells and small cap hydro don't perform too well, someone stands to make a tidy profit putting a green tint on the power bill.