CALGARY, Alberta—When Mayor Naheed Nenshi broke ground on Brookfield Place, this city’s signature skyscraper project, he said the energy capital was “well into an arms race” of tall-building construction.

That was in the fall of 2013, amid a boom fueled by high oil prices that had the commercial real-estate market in Canada’s oil capital rivaling that of Houston. Space was in short supply, vacancy rates were in the low single digits, and rents commanded a premium. The groundbreaking on Brookfield Place came not long after...