Here's how we operate in practice: we have federal-provincial cooperation agreements with a number of provinces. This kind of agreement has been in place with the Government of Quebec since 2004. Under these agreements, when federal and provincial proceedings are triggered on a single project, the two levels of government work together to conduct a single environmental assessment that generates relevant information so those levels of government can make their decision together.
On May 5th, 2010. See this statement in context.