Yup, so, All criminal law is federal, but that doesn’t determine enforcement jurisdiction. Constitutionally, administration of law and justice is provincial.
In Ontario, yes, if a municipal agency falls short it falls to OPP. In Nova Scotia, the Police Act establishes the existence of the Nova Scotia Provincial Police and sets out all their responsibilities. Then there’s a section that lets the province enter an arrangement with RCMP to be the NSPP, and of course that’s what presently exists. So yes- if municipal police in Nova Scotia can’t handle something, it goes to the Mounties acting as provincial police. But not to their federal policing branch, save to the extent they may borrow some federal bodies temporarily in an emergency to put on a uniform and do patrol stuff.
Now, the RCMP do federal policing everywhere in Canada- stuff like national security, border, transnational organized crime, major cybercrime… Some of this overlaps provincial responsibility (cybercrime, drugs), some does not (national security, border). There’s further nuance in who prosecutes (fed or provincial crown) too.
If the federal government establishes certain law enforcement priorities and wants to augment with federal policing because of the national/international scale, to an extent they can… I guess for a simplistic and non-contentious example, if the Mounties wanted to take on interprovincial human trafficking as a federal policing initiative they could so so in parallel to the provinces and municipalities. But mostly there’s not much overlap anymore except at higher level organized crime.
Sorry, you got me nerding out. Did I hit what you were actually asking?