There currently are a variety of options to travel by night train from Toijala (Finland) to Rovaniemi (Finland), taking between approximately 8 and 13 hours: Namely the Yöjuna 273, the Yöjuna 933 and the Yöjuna 267. These lines are operated by VR.
VR, Finland's national railway operator, runs passenger trains throughout the country, including overnight services to northern Finland.