Hi!!
It's nice that you show such intrest towards Finland! I really hope you will enjoy your time here even though the winter novadays is what it is...
Well about the tyres.. Studded tyres are most common here... but renting tyres is not possible 

 at least I've not heard of such thing.. as known studded tyres are good with icy road and tyres without studs are a bit better on snow.. But with heavier vehicles I recommend studded tyres. You can find second-hand tires also that are cheaper.. Also depends on the tyre size.. bigger size brings more price naturally.
Best regards,
Tuure