Hikers may cross Finland's international borders with Norway and Sweden anywhere, as long as their passport allows them to travel in these countries, but certain goods must be declared with the Norwegian customs (www.toll.no) before they are taken into Norway. The Russian border can only be crossed in certain places. Visitors entering Russia need visas. Special permission is needed from the Finnish Border Guard (www.raja.fi) for hiking in the Finnish-Russian border zone.
If you cross state borders with dogs or other animals, read the rules from pages of the Finnish Food Authority (www.ruokavirasto.fi) and Swedish Customs (www.tullverket.se).