Alberta could replace the RCMP with its own provincial police force without separating.
Stated by: Government of Alberta
Summary
This is correct and already done elsewhere. Section 92(14) of the Constitution gives provinces authority over the administration of justice, which the courts have read to include running provincial police forces. Ontario, Quebec, and Newfoundland and Labrador operate their own provincial police; the other provinces and territories instead contract the RCMP to provide that service. Alberta could end its RCMP contract and stand up its own force as a matter of provincial choice, with no need to leave Canada, though doing so would carry significant cost and transition issues.
Evidence
Section 92(14) gives provinces jurisdiction over the administration of justice, which courts have interpreted to include authority over provincial police forces.
Library of Parliament (distribution of powers) (opens in a new tab)
Public Safety Canada confirms provinces can establish their own police service, as Quebec, Ontario, and Newfoundland and Labrador have, or contract the RCMP, as all other provinces and territories do.
Public Safety Canada (contract policing) (opens in a new tab)