And there is not THAT many axis through Finland and Sweden a Russian advance can take to reach Tromsų and Narvik. I served in the border guards in the 90s, and we had the war role as regimental recon. Outside of the roads, Finnmark (The region east of Tromsų to the border) is one of two things:
1. Mountains
2. Peat bog.
I did a bit of map study on the topic