This heavily depends on the type of train you are planning to use.
In general there are 5 different type of trains you can use with your Interrail/Eurail pass
There are the following train categories operating in finland:
You can actually find details on reservations organized by country on interrail.eu
Credit:stackoverflow.com‘
5 Mar, 2024
4 Mar, 2024
4 Mar, 2024