I like to travel with my DSLR and I have nice slingshot bag for it which I can take with me on the plane along with my carry on. This picture shows what I want to do while boarding the plane. Would it be OK/legal for me while flying from Canada to USA?
You shouldn't have an issue, I've flown with my Manfrotto + ball head (the one with the leg warmers) all over the world, including the US and it was never a problem. The only time you should really consider a tripod is when entering a train station, or other places where photography is restricted without a permit of some kind. In those cases, pack a monopod :)
You should be fine, however unless you're not planning to check luggage you may want to consider tossing it into your checked bag.
My manfrotto tripod is 25.79 in when closed, without the head so it's just easier for me to pack it in a bag. If you do decide to carry-on make sure you're comfortable moving in a crowd with the bag and tripod. Make sure it will still fit in an overhead bin. And, be ready for security to be worried that you're carrying a large club, just in case.
You should not have a problem, from my experience most airlines allow two carry-on articles. As long as the requirements are met, you should be fine. Here is an example for Air Canada's Rules