There are 5 provinces on the map that are always considered to have a canal, when connected to certain sea zones:
Con with BLA & AEG
Kie with HEL & BAL
Den with SKA & BAL
Swe with SKA & BAL
Nap with ION & TYS
These are the 5, and the only 5 like this. So even tho Swe does not have a canal in the normal game, so long as it is connected to both SKA and BAL, a fleet could enter Sweden from, say, SKA, and exit via BAL. This is even if Swe gets connected in funny ways to the mainland.
This, and more bits like it, can be found here:
www.dipwiki.com?title=Seismic
-mike