You can catch from Narvik a train via Kiruna. Boden to Lulea :)
From Lulea you can use included Buses via Happaranda/Tornio (Twin border towns) to Kemi (Finland) From Kemi you have railconnections to Rovanemi, Helsinki,Turku, Oulu :)
The leg Lulea - Happaranda can be done since few months by train too.
Thats in the far north-above the Botnic sea. I just read that they will electrify also the short line inside FI and make a train connection again all the way-to start 2024.
For now there is just a short section (about 20 kms) to cover by bus-there are NO buses from sat/midday till sun/midday. There are 2 companies, 1 of these accepts IR. There are also a very few direct BUSlines from the upper north of NO into FI, but these are quite expensive.
There are also numerous-and some very luxurious and still quite cheap- ferries over that sea between Sverige and Suomi (Finland). Some give discounts to passholders. Viking and Silja/Tallink are best known and biggest.