The surface and skies of Earth have been heavily polluted through various issues. Climate change, war, biological/chemical warfare, nuclear weapons etc. The sky is blanketed in a permanent semi opaque cloud cover that allows just enough reliable light for farming in some areas. It's been discovered that new clouds/mist in the upper layer are forming over certain areas, causing certain lands to become darker in general as another layer of cloud travels the globe. There's consistent ashfall as well as acid rain over the lands. Soil across the planet has been ruined or desertified, however a few factions have been slowly recovering the land around them over the span of multiple decades.

All this contributes to colder temperatures on Earth, making open air farming harder, but it can be assumed that the planet isn't going to get any colder anytime soon. Despite that, human civilization has yet to collapse. Infact across the planet small countries, city states, camps etc still exist in places capable of sustaining life.

One such faction is a small country in the northern Canadian and Alaskan region. Due to the frigid temperatures, blizzards, snow, ashfall etc they are unable to maintain consistent open-air farms.

Thus, they have turned to a method of farming that is best suited for their environment (ie aquaponics, hydroponics, aeroponics, etc).

Assuming that they have the ability to import topsoil, artificial soil, nutrients, fertilizer, seeds, and chemicals; what type of alternative farming (nontraditional open air) would such a country have chosen to utilize for growing crops on mass?

Crop yields need to be large enough to feed a small country. Exporting isn't as much of a priority.

Some major requirements are that they have to be able to maintain the farming system during times of war (common), economic upheaval (outside their borders), sanctions, periods of harsh weather (longer blizzards, ash/acid rain, cloud coverage getting thicker, general pollution, water toxicity, etc). The solution doesn't have to outright hit every requirement from the start, rather the solution should have a feasible way of addressing such issues without causing major issues or entire redesigns of farms.

The country in question has total access to manpower, as well as its power grid for farming at any given moment. They are also more than willing to throw as many resources as they can into it. Technology is near future.

Some restrictions: Getting above the cloud layer for extended periods of time is impossible. Satellites do not exist, and no faction has the ability to send one up (not a technological limitation). Furthermore, predicting weather related issues from cloud coverage is impossible unless one is tracking an in-progress issue and projecting its path. Alliances and trade deals are almost always ad hoc, nothing is forever guaranteed, but existing contracts are respected and fulfilled.