Here's my 2 cents worth. I'm in the process of building my first kayak,
so take it with a grain of salt.

I'm using 1/8" maple on my Cirrus. I was planning to use a mix of
white oak and maple but I ended up with problems with the white oak.
The oak plywood had voids in it, and also had a low grade backing on
it. The backing made it hard to work with, and one of the panels
broke when I was trying to move it (probably because of the voids).
I ended up giving up on the oak and going with all maple. That's
not to say you can't get good oak plywood, but the place I bought the wood happened to have some really good maple, with a maple back and no voids in the core.

It's possible that you could still get away with plywood with voids
in it, if you're going to glass the deck and if you're very careful
when handling the 19' long pieces. But it's also possible to find
wood other than okoume that is void free.

Let us know what you decide on, I'd love to see pictures.

Chris