I've used a lot of white pine for strips, but never for gunwales. It can be found easily in long clear boards, but I think it is too soft. Poplar is a surprising wood, light but strong. Keep in mind that it doesn't do well with water, so I would seal all sides of it with epoxy .1. Is white pine legit/viable as a gunwale wood? I was thinking it was not, but Conk mentions it above and obviously he knows what he's doing. I know it's light, and as easy to find as a gallon of milk.
2. How good is poplar? Is it comparable to spruce in terms of strength/weight? Doug and Conk both mention it. Can one get away with say 5/8x5/8 rails on a 16' boat that won't be abused?
I'm sure Maine has tamarack. I've been itching to try that for gunwales too. It is difficult to work with, but would look pretty amazing, and be quite water resistant too.