I have read on the internet about this prosject.
So what do we think about this?
It's seems like it will be build with track guage 1435 milimetre
This will be a further expension of Rail Baltica (
http://www.railbaltica.org/) which is a planned railway route from Warsaw to Tallinn.
https://www.railway-technology.com/projects/helsinki-tallinn-railway-tunnel-gulf-of-finland/
https://emerging-europe.com/intelligence/tunnel-vision/