Hi ,
Ive driven to Finland numerous ways.
Dfds from Harwich to Hamburg then Ferry to Helsinki
DFDS from Newcastle to Gothenburg then ferry from Stockholm
Dfds to Hamburg, then drive through Germany, Poland, Lithuania, Latvia and Estonia.
Thoroughly reccomend it. bit of an expedition in itself but you will see some great places/
Just make sure your car is up to it ( not like the clapped out Transit van I normally Take)
Feel free to e-mail me for route advise