In generic terms and in practical application within Canada, a metropolitan municipality is an urban local government with partial or complete consolidation of city and county services.
The former Municipality of Metropolitan Toronto, 1954-1998, was created by partial amalgamation of the City of Toronto with neighbouring towns and townships in southerly York County, from which the metropolitan municipality was then extracted.
Each jurisdiction retained a degree of local autonomy, like the City of London and the boroughs in Greater London, while the Metropolitan government replaced the old county government and supervised metro-wide services, such as police, fire and ambulance.
As with metropolitan municipalities, sub-regional communities - cities, villages, townships - within the regional municipality retain a degree of local autonomy, with the regional government focusing mostly on shared public services (police, drinking water, etc.).
These may be formed by presidential decree in any province with a provincial population (city center + outlying districts + villages) exceeding 750.000, as per the law governing metropolitan municipalities.