Hi
A buddy of mine from the Chain Gang told me about your question. I live in Helsinki.
The state of the roads here is highly variable since the country is pretty long north-south. At that time of year you will probably have wet/icy conditions in the south, but as you head further north the conditions will change into pretty hard winter.
They use only grit (sand) in most places, very little salt. Studded tires are a requirement for all cars during winter. I've only driven there 2x in a car, but you can expect hard-packed icy snow in a lot of places, if not must.
The main thing you should be very careful of is reindeer! Whereever they DO apply salt, the reindeer will sit in the road and eat it. So as you can imagine, the safety benefits of salting are offset a bit by large numbers of animals in the road way.
My guess is that, as you head north, the road condition will be pretty open and maintained all the way to Rovaniemi (at the arctic circle). After that civilization gets pretty sparse and road maintenance drops accordingly.