Generally there is no problem flying a four piece rod, without reel, as carry on. But like a lot of carry on rules today, a lot depends on who is working the security check point at the time you pass through. I have gotten flack about metal rod tubes, like from Winston and the Orvis T3's. Other times I have only gotten the comment "wish I was going fishing."
Flying out of Canada, they apparently have the procedure of stopping you, getting a supervisor and then hand checking everything again if you have any unusual carry on items. They for sure will not let you carry on line, leaders or backing.
The best solution I have found is to purchase one of the new rolling duffels that have a dedicated space in the bottom to hold several four piece rod tubes and check it as luggage. Orvis and Cabela's both have luggage with this feature now.
One other solution is to Fedex or UPS your equipment to the lodge or hotel ahead of your arrival and arrange for a prepaid pick up after you leave. This also offers better insurance coverage than hassling with an airline if something is lost.