There are agreements between the Government of Quebec, the Government of Ontario, and the Government of Canada. Instead of having the snowplow from the Quebec government go to halfway on the bridge and then pull up the blade, the Government of Quebec has an agreement with the Government of Ontario and Canada. The Government of Quebec plows one side of the bridge, let's say going southbound, and the Government of Ontario maintains the other side, going north. It's an internal agreement.
On December 7th, 2009. See this statement in context.