Finland is not a climbing destination by itself, but if you are planning a trip here anyways, there is plenty of rock for a whole summer! The climbing season is generally from when the snow melts and the cliffs dry up to until they get wet again. Crazy boulderers do go climbing even during the winter (better friction!!!) but a lot of us are content with training inside until it warms up just a little bit!
I recommend that you visit either The Mountain Shop or Camu in Helsinki, the day you arrive, and go buy the Suomen Kalliokiipeilyopas 2003. It is about 35€, but it has driving directions and route names, grades and locations on the cliff nicely drawn. It includes pretty much everything you need to know to climb at any crag in the book, which includes pretty much all the good destinations for roped climbing. Boulderers can find information on the internet or find someone to show you around, since the best boulders are not in the topobook. Slouppi is a good place to start, use their forums to locate people in the areas you want to visit, or are staying in.
There wont be a lot of route information on these pages since it would basically be stolen right out of the topo book and I am only adding information for climbs that I have been on. Use this information in conjuction with the topobook, since this database has information on protection and the quality of the climb, while the topobook will show you the location and line, as well as driving instructions and so forth. There will be links to complete topos on the web, if they are available.