We played today the first encounter of Sea of Blood using the "Revenge", an NPC ship, sharks and cannons.

It was a test encounter, just to learn and try the new rules, we made a lot of errors but the big question was:

does a shark or a figure in water blocks the line of sight of the cannons or the other figures ?

On the rulebook I hanen't found nothing secial about this, so I would say yes, but it seems so odd ...

And another question: can a hero make an aimed attack with a cannon ?

Yes to both. It also doesn't make sense that a ship doesn't block line of sight, but the alternative is an overly complex system of checking for elevation changes in the middle of one's line of sight. It would be more realistic, but probably not worth the hassle.