There currently are a variety of options to travel by night train from Haukipudas (Finland) to Helsinki (Finland), taking between approximately 9 and 12 hours: Namely the Yöjuna 266, the Yöjuna 274, the Yöjuna 276 and the Yöjuna 264. These lines are operated by VR.
VR, Finland's national railway operator, runs passenger trains throughout the country, including overnight services to northern Finland.