It's great in my opinion that Poland is doing this. It will put people to work helping the economy and make Poland more independent.
It's not so simple, because things must have potential of future saving/earning to be economically justified, nut just work for the sake of work creation.
It's happening probably since 20 years, that from time to time Russians forbid Polish ships to cross from Zalew Wiślany to Baltic Sea through their territory. This channel will give independent access to the sea to Elbląd - 4th largest city on Polish coast. Maybe it will be a boost for port/shipping investments and industry there, when Russian risk will disappear. But only maybe, if not, then it will be mostly wasting of money, which could be used in some more useful way.