Baltic birch is much better wood, but it is heavy compared to Okume.
Baltic also has interior glue. Unless you coat it with epoxy you can expect the glue will fail with prolonged water exposure. Actual Baltic Birch is much better than the fir I had since it had no interior voids in the plywood and the basic wood does not chip as easily.

Marine Okume (also known as Gaboon Mahogany) is best for kayaks and light boats. It still needs to be protected - varnish will do for most boats. BS1088 specification. Joubert is the brand name I'm familiar with.
Meranti is also available at slightly higher strength and higher weight, but is usually made to a slightly lower specification grade BS6566. Aquatech is one brand name.