As far as i know, Int is what lowers the chance the monster will resist your spells.
for corsair this is our Quick Draw. They can be resisted. and we'd need INT since we don't get a Skill like other "casters."
I dont see COR piling on INT though. maybe swap INT rings and stuff for a Quick Draw Macro. aside from that though, keep focusing on what a marksmanship ranger would focus on. til 70ish anyway.