A read of the RCMP Act shows that this isn‘t specifically ruled out but it does give the Commissioner the authority to institute other rules and regulations "for the organization, training, conduct, performance of duties, discipline, efficiency, administration or good government of the Force."
Para 4 of the Act also states, "The Force may be employed in such places within or outside Canada as the Governor in Council prescribes." which tells you something.
Para 18 d reads "to perform such other duties and functions as are prescribed by the Governor in Council or the Commissioner." They too, are subject to being "called up" for duty.
Then there is Section 12.1 which states "Every member who has contravened, is found contravening or is suspected of contravening the Code of Conduct or an Act of Parliament or of the legislature of a province may be suspended from duty by the Commissioner." Get charged under the Code of Service Discipline and get suspended. Of course, reading this you could also be suspended for being give a provincial traffic ticket. Not sure how Provincial Police Acts deal with this.
Lets not even get into the issue of Commissions.
My take on it is the RCMP are already burdened with obligations that other police forces and agencies aren‘t. From my take on it, it‘s para 18d that is really the issue though since it would be a dogs breakfast if both the RCMP and the members Militia unit would be called up at the same time, no matter what MOU was in place beforehand.
Having said all of that, the RCMP
now permits it‘s members to join the Cadet Instructor Cadre. Of course, there really isn‘t much worry that these guys will ever be called up.