Following the ongoing debate over at the Royal Swedish Academy of War Science’s blog regarding what role infantry could have in fighting a mechanised attacker in Norrland, a Twitter-exchange erupted following a comment to the end of who the mechanised attacker would be? Surely the Russians would have better things to do with their mechanised units than to try and capture vast expanses of forests, fells, and bogs? The question deserves a closer look, as the answer by default holds significant importance to the defence planning of not only Sweden, but Finland and Norway as well.
Norrland is not of interest to the Russians due to anything found there (no, not even the Kiruna iron ore), Russia has enough undisturbed wilderness of its own. But the region is very interesting due to the proximity to the Kola Peninsula.

The Kola Peninsula, and more generally the Murmansk-Arkhangelsk-Naryan-Mar area, are of immense strategic importance to Russian defence planning due to their role as the sole route from where to break out into the Atlantic to intercept the transatlantic supply lines of NATO, as well as providing the basing area for the majority of the Russian strategic nuclear forces. In particular the Russian second-strike capability is centered around the ballistic-missile submarines of the Northern Fleet (though a limited number is also found in the Pacific Fleet), and they would take up position in the Barents Sea from where they would fire their missiles in case of an all-out nuclear attack on the USA. In addition, the shortest airborne route between the US and Russia passes over the Arctic, meaning that the area plays a role in long-range aviation as well.
This leads to the Cap of the North (or Sápmi) being the left flank of the Russian strategic deterrent and the frontline of any attempt at stopping the US from reinforcing Europe. Geopolitics plays an interesting role as well, as Norway is the sole NATO country in the region. While it is highly unlikely that Norway or other NATO forces would try and attack the northwestern corner of Russia due to the risk of escalating a conflict into full-scale nuclear war, Russia could conceivably want to push the frontline westward. As far as Russia is concerned, for the moment there is no real strategic depth to protect their bases. The Norwegian town of Kirkenes lies only 150 km from Severomorsk, the main base of the Northern Fleet. This is well within firing range of the MGM-140 ATACMS used by the US M270 MLRS and M142 HIMARS systems. And once the front is being pushed westwards, the question where to stop remains open. Capturing e.g. Narvik and Bodø would significantly hamper the ability of NATO to recapture Norwegian territory, while at the same time providing forward bases from which to operate against the transatlantic supply lines (compare German plans for submarine bases in Norway during WWII, rendered utterly insignificant by the fall of France).

But Norway is a tricky battlefield. The country is relatively narrow and heavily mountainous, handing a relative small defending force near-perfect conditions to defend against a more numerous attacker.

Which makes flanking tempting.

There are three possible ways to flank the Norwegian Army, either by amphibious and/or airborne landings, or by marching through Finnish Lappi and Swedish Norrland to reach (or threaten) the Norwegian coast.
Now, cutting through Finland and Sweden to reach the Atlantic coast is no simple endeavour, the shortest way from Severomorsk to Narvik is a nice even 1,000 km, passing through Sodankylä, Pajala, and Kiruna, before following the Iron Ore Line to Narvik, the northernmost railway in western Europe. The roads are of varied quality, and getting any kind of a workable supply line through the region will be a challenge. The railroad networks are a chapter of their own, with the Finnish tracks not being connected to the Russian ones north of the Vartius-Kostamus crossing, and there being a gauge break between the Finnish and Swedish railroads.
However, the most distinguishing feature of the region is the sheer amount of real estate. Combined with the fact that for none of the involved countries, with the possible exception of Norway, will the northern theatre be their main front. While a Russian offensive undoubtedly could allocate more forces than the opposition, it is still highly doubtful if they would be able to muster a large enough number that they could lay down a solid frontline and protect the rear areas and supply lines. As such a likely scenario is that the Russian spearheads would be able to make some impressive mileage while battling bigger and smaller skirmishes, while the real decisive fight will be a drawn-out one between security forces and smaller Finnish and Swedish units blowing bridges and targeting enemy supply units.

This is not without precedent as the fragmented battlefield is nothing new to northern Europe. In January 1942 two Finnish battalions (1,900 men in total) infiltrated 75 kilometer through enemy territory to May Guba, burned a major supply depot, and skied back to own lines with a total loss of 3 killed in actions and 10 wounded (in addition to scores of frostbitten soldiers). During the whole of the Continuation War large parts of the frontline north of Lake Onega were if not fragmented then leaking, and as it is likely that the main Finnish and Swedish units will be concentrated towards the population centras in the southern parts of their respective countries, a return to the same scenario would not be unlikely in case of an armed conflict.