You would think that Canadian jurisprudence had developed a clear objective rule for settling even the trickiest “double aspect” issues, wherein both federal and provincial governments can claim that some crumb falls within their respective spheres of constitutional power.
You would, apparently, be wrong.
Actually, though, no one has ever been able to predict how the Supreme Court of Canada would determine federalism cases. It's a mess, and it's been that way since Duplessis was unable to stop St. Laurent from abolishing appeals to the Judicial Committee. Since that time, the Court has been split between the terminally confused and those who never wanted to strike down any legislation, provincial or federal, on division-of-powers grounds -- a position more-or-less adopted by the SCOTUS after the 1930s and defended for Canada by Paul Weiler.