So, I got the Caf? PWP the other day, and I'm not sure where I want to put it.
My campsite is in the top left corner, and my house is just above retail so I can't put it there.
In the little dip near the waterfall leading into the sea.
edit: But, personally, in my town (I have the same layout as you), there is a little dip in the cliff overlooking the sea and not the sand (well, half sea, half sea and sand, if you know what I mean :3) and the cafe fits nicely in there.
Personally I like the little secluded area near the waterfall on the left side of town; unless that's where you meant your campsite is. In that case, I'd say across the river, but below the plaza
You also might want to keep in mind whether you want PWPs around it, like for example I always like a little parkette with a bench by my cafe. I like by the left waterfall too, maybe put some trees behind and a bench in front.