Provinces are able to regulate emissions that occur in their province, but what they're unable to do is deal with impacts that occur outside their province.
Similarly, if there's a large project in the U.S., air generally flows west and north in Canada, so if you're in Quebec, northern Canada or the Maritimes, most of the pollution you're getting, or much of it, is coming from upstream. It's coming from the U.S. Midwest. It's coming from Ontario. It's well documented, the phenomenon called the grasshopper effect, where persistent organic pollutants, toxins, make their way up to the Arctic. You actually find toxic substances in the body tissues of people in the north that are higher than those in the south because the air pollution generally moves east and moves north. Quebec, the north and the Maritimes, particularly, are upwind and are affected by these problems.
They are unable to deal with the upwind or upstream causes of pollution. Pollution crosses borders. It doesn't stop. That's a core role of the federal government and it has been since the early 1970s. The feds passed the first Clean Air Act in 1971. This is an area they have occupied for over 50 years, and we need them to continue to do so.