The Year of the Hare by Arto Paasilinna. The classic Finnish novel of a man who walks away from his city life and disappears into the northern wilderness with a wounded hare. Funny, deadpan, and gives a strong sense of how Finns relate to their forests.
Winterkill by Marc Mason. A Finnish-Lapland crime novel that captures both the cold and the strange light of polar winter. Easy reading, atmospheric, and useful for the mood as you drive in.
The Sámi People: Traditions in Transition by Veli-Pekka Lehtola. A clear, sympathetic overview of the indigenous people whose herding cycle still defines this part of Lapland. Worth reading before any visit to a reindeer farm.
Travels in Siberia by Ian Frazier. Not Finland, but the closest thing in print to a feel for the vast taiga that begins just across the border. The Saariselkä fells are its western edge.