I always use epoxy to join the wing halves, but have used both epoxy and CA for fiberglassing the joint. I think the epoxy for joining is a good idea because it will fill small gaps where the wing isn't perfectly flush with its mate better than CA. Also the CA tends to be more brittle, but I'm not sure that's really a factor in a good joint. As previously mentioned, the epoxy gives you several shots at perfect alignment, too. I would imagine if the mating surfaces are perfectly true, either would do just fine. But always glass!