I did the flat far north in 2006 - right up to the Finnish/Russian border on the coast near Murmansk. Wild camping was easy and stunningly beautiful, but the mosquitos in summer are scary. However, swimming in the lakes and rivers before brewing up some tea in the evenings was lovely beyond words. Watching naked women climbing out of the lake and strolling to the campsite sauna is good for the soul, too!
I did have a mental problem, however, with the trees. There are trees everywhere, obviously. You can only ever see trees and the road ahead - the horizon is invisible because the land is flat and the trees are so high. It really wore me down after two weeks, although I can do deserts and stuff without any problem. I eventually made a run for the Baltic coast and had a much better time.
Do a coastal route. I'd say.
Edited for stupidity (blame the trees...) the border at the northern coast is Norway/Russia. Finland starts a wee bit further south. Doh!
