The only state that Alberta borders is Montana, which has the following criteria to call a place a "city": 'A municipality with a population between 1,000 and 5,000 people is a Third Class city. A municipality with a population between 5,000 and 10,000 people is a Second Class city. And a municipality with a population over 10,000 people is a First Class city.' -from
https://en.wikipedia.org/wiki/List_of_cities_and_towns_in_Montana
From this list, 3 candidates emerge: Browning, Cut Bank, and Shelby. Using map app, Browning (2010 population 1,016) proves to be the winner (by 6 air miles, over Cut Bank, pop. 2,869) at 178.3 miles as the crow flies, 206 miles by road.
If the closest "First Class City" of population over 10,000 (the population required in Alberta to be eligible for city status) was desired, then Kalispell (pop. 19,927) is closest, at 197 miles by air. It also turns out Whitefish was a second-place candidate among smaller cities, at 183 miles by air.
