Simply put, Sweden and Norway share the Scandinavian mountain ridge which gives a lot of rain at altitude and dammable valleys; Finland is on the whole much flatter, so has less favourable conditions for hydro power.
> I have to do some reading, but my understanding was that the Finnish plant is using an alternate funding structure from many of the existing nuclear installations. Less direct subsidies or more risk directly on the commercial entities?
Haven't checked recently, but at a guess / from vague memory: Probably shoving off as much as possible of the financing onto the builder / owner, Rosatom (mainly via its Finnish "partners" / subsidiaries), but in the end backed up by State guarantees because who else would voluntarily/ is big enough. All of course dressed up in more or less convoluted arrangements as suitable to make it look a little better / less bad.
(What, me cynical?)