I think the general idea is that the 'bridges' aren't so much intended to be bridges, as you don't need a fleet to cross the water. Think about it... the British evacuated out of Dunkirk mostly on fishing vessels (of course, that was in what in game terms would be Friesland).

But I think the idea there is how tough would it be to commandeer local vessels to make the crossing.

And I don't know if it makes sense to put a land bridge between Finland & Sweden. It would be pretty tough to lead an army through Kemi down to Stockholm in the middle of the winter.