The elevation in metres (m) refers to the elevation of the observing location above mean sea level. The elevation of each site is given to the nearest metre and is generally the height of ground on which the instruments are exposed. Prior to April 1, 1986, the elevation at principal stations located at airports was generally the established by the elevation of the aerodrome. For principal stations not located at airports the elevation was established by the elevation of the barometer cistern.
Government of Canada - https://climate.weather.gc.ca/glossary_e.html