Reed and Cane should never be sealed with any kind of polyurethane since it's a natural material. It needs to be open to the air to "breathe".
Reed can be finished with "Weavers Stain".
Fiber Rush can be sealed with shellac. Instructions are in the fiber rush booklet.
We recommend that you use Binder Cane to weave chairs that will be outdoors on a porch. Don't seal binder cane. It has a natural bark finish, and as mentioned above, cane and reed need to be able to breathe or they will dry out and break down a lot faster than if left in their natural state.
If you absolutely prefer to use Reed for a chair left on the porch, Thompson's Water Seal has been recommended to us as a sealant.