Sitka Spruce is the favored wood for spars, including spreaders. Be sure to
varnish it thoroughly. (Varnishing is better than painting because it allows you to see where moisture may be getting through to the wood and causing rot.)
If spruce isn''t available, a good piece of cedar may also work. It seems to have better rot-resistance than many other woods. For further input , you may also want to try asking his on the Woodenboat forum.