If you can, try GENTLY inserting a shim or two to spread the crack enough to surgically insert some ext glue, remove shim, then clamp. If not, epoxy is about the only option I can think of.
Since this is your railing, you probably have time to dutchman a piece in and then you can re-stain/finish. Epoxy works, and can be aesthetically pleasing and is quick, but to me it always looks patched.
Tim