The Helsinki-Tallinn tunnel would be expensive, but in the current climate of hostilities with Russia, the EU could support it just to make a point.
It would also enable high-speed services from Finland to Central Europe - Rail Baltica to Tallinn is currently being built, so Helsinki-Warsaw could be a plausible connection, doable in less than 8 hours. (More than ideal, but trains that run for 8 hours from one end of their journey to another are commonplace in Central Europe.)
It would also enable high-speed services from Finland to Central Europe - Rail Baltica to Tallinn is currently being built, so Helsinki-Warsaw could be a plausible connection, doable in less than 8 hours. (More than ideal, but trains that run for 8 hours from one end of their journey to another are commonplace in Central Europe.)