[Nick_K]

I usually specify enemy nations and don't include sea nations if I don't want to have to fight one. I've never liked big maps myself, although of course if they're your thing then that might help.

I can't see a way of beating an impossible AI sea nation with a land one early in the game - perhaps something could be done with SCs?
Of course, if you keep your coastal province PD high and station troops there early then you may be able to stop them from attacking in the first place.