Good2Golf said:
The Ministers of Public Safety and National Defence generally are the two key officials involved - both federal.
As usual for Canada, it's a little more complicated than that.
First of all, we have to know that Canada has a single Criminal code, enacted by Parliament, unike the US which has 51 different ones (one per state and the Federal one). Since that code defines the powers of peace officers, our police officers are technically police officers anywhere in Canada (So much for running to the county line "Dukes-of-Hazzard" style to foil the Sherriff).
This said, the administration of justice and public safety/security are Provincial responsibility, so the provinces - not the Federal governement - are responsible for providing police services and natural disaster relief in their province. The Federal Minister of Public Safety is responsible only for overarching national security: national level criminal intelligence, security on Federal properties, border security and policing for purely Federal acts with criminal level of infractions (Controlled Substance Act [drugs], Firearms Act, Customs and Excise Acts) through a Federal police - the RCMP, and provision of police services to the Federal territories (Yukon, N.W.T and Nunavut).
So policing in the various provinces is provincially provided. The two largest provinces (QC and ON) do so through their provincial police forces and various municipal forces. The other eight provinces have elected to do so by
contracting for the services of the RCMP provincially and having municipal police forces for the large municipalities. Don't be fooled: These RCMP forces working on contract for the provinces are answerable to the provincial Department of the Attorney-General, or their equivalent in each province. These RCMP "sub-forces", so to speak, operate in their own province only and coordinate with other provincial forces as if they were for that province only. Of course, when two provinces have to work together and they both use the RCMP, it makes coordination easier - but they remain separate entities.
BTW, this set-up explains the schizophrenic nature of the RCMP, with the bulk* of the force made up of small town/country police officers and the national group made of high-end, complex criminal investigators and security experts, but nothing in the middle as they are without working knowledge of large town/cities policing and investigations realities.
So, going back now to assistance requests for police matters or natural disasters: It is the provincial public safety ministers that make the requests (the RCMP cannot ask for such assistance directly except for Federal level matters) to the Federal public safety minister. Now here is the thing: once the request is made, the Federal
must provide assistance, but it is the CDS (upon consulting with the M.N.D.) that decides what help he/she can/will provide, because, once provided, these military forces now work under the authority of the provincial ministry of public safety - not the Federal one (i.e., they now answer to Her Majesty the Queen of [insert province] as represented by the Lieutenant-Governor-in-council of that province). For instance, during the Oka crisis and the October crisis, the troops deployed in Quebec were under provincial orders. The beauty of the system is, if the Federal level feels that the province wants to misuse the troops or use them for improper purposes, they can send "assistance" that won't really help**.
All this to say that, in legal effect, we have the equivalent of "Posse Comitatus" because the CAF can only be deployed in a province under that province's orders and direction - they become in effect like US State's National Guard but in Canada, instead of having provinces have their own, they borrow them from the Federal governement. There are, of course, very limited purely Federal cases. For instance, the forces deployed at the border last year to deal with influx of refugee claimants entering from the US - as this was a Federal matter (border security), or the troops deployed to protect Parliament during the October crisis, which remained under Federal jurisdiction.
*: If all provinces were to terminate their contract with the RCMP and set up their own forces, about 75% of RCMP officers would have to be laid off.
**: For instance, if a province wants troops to help "quell riots" that really are just peaceful demonstration against the current Premier - but really just want to use the troops to scare them into silence, the CDS (upon advice) could send that province the Naden marching band, or a field ambulance unit.