The question of how to get to Ruka is decided depending on what kind of transportation you prefer to use. Most often tourists fly to the international airport in Helsinki, from where the local carrier Finnair departs for Kuusamo every day (twice a day in winter). After an hour and 20 minutes you will be at the resort's airport where a regular bus will meet you. It will take you to the center of Ruka.
From Helsinki you can get to Ruka by car on highway E75 and 5 via Kuusamo or Oulu (800 km). Also from the capital of Finland you can take a train to Kemijärvi, Rovaniemi or Oulu (6.5 hours), from where you can take a bus to Kuusamo (2 hours) and change to a bus to Ruka (30 minutes). By the way, the Helsinki-Kemijärvi night train allows you to carry a car with you.
