Loading and unloading a standard canoe should actually be easier than with any other kind of boat, including inflatables if the time you spend is worth anything to you (loading rigid kayaks can also be pretty easy if you invest in rollers, or if you simply lay it on padded bars). As tjalmy pointed out, canoes should be lighter than “comparable” kayaks and in my experience they always are. Of course, real light weight comes with a higher price tag, so the cheapest canoes are also the heaviest (besides being the poorest performers in most cases).
So, let’s say you end up with a moderately heavy canoe, one that’s maybe 65 pounds. How do you lift it onto your car’s roof? The answer is that you don’t lift it up there. Not all at once. Check out the picture below.
That’s not a canoe but the idea is the same, and that’s the position you want the boat to be in when you start loading. Two people can do that while never lifting more than half the weight of the boat any higher than their waist. Put one person on each side of the boat, carry it waist-high, and simply tilt the boat so one end is higher than the roof rack, and then set the boat down (so it’s like the boat in the picture except without that wheeled contraption you see there). From there, you just pick up the low end and slide the boat up the rest of the way. By the time the boat needs to level off on the rack and your hands need to be head-high or so, the boat is balanced pretty well and virtually no lifting force is needed at all. The heaviest lifting of the whole process is with half the boat’s weight carried by each person with their arms down low at their sides, and virtually anyone can do that.
If the rear bar of your roof rack isn’t close enough to the back end of the car to lean the boat against as shown here, you can simply avoid setting the other end on the ground, so that the slope of the boat is flatter and it contacts the rear bar and not the roof itself. Then the two people can hand-walk their way toward the rear of the boat (and the weight lifted gets less and less as you do that), before pushing the boat all the way onto the rack. If the front bar is closer to the front edge of the roof than the rear bar is to the back edge, you can load more easily from the front end of the car.
You can load this way with one person on each end of the boat, but in that case, one person will need to lift their end up high. That’s still a huge reduction in effort compared to what most people do since only the stronger person needs to lift their end high (what most people do is lift the boat high at both ends and move it onto the rack from the side, but the problem there is that both people need to be fairly strong and fairly tall), but as you can see, there’s really no need for either person to lift their full share of the load any higher than their waist.
Oh, it should also be mentioned that if one of your cross bars can extend out to one side, that will eliminate any problems with leaning the boat against the bar but possibly being in contact with the roof. That method might be what you meant by a canoe loader.
If you shell out for a nice, light canoe, you can use the same loading methods but the whole process will be even easier.
Regarding rentals, I always say this, but it’s a rare outfitter that offers canoes that are anything but the worst you can buy, or maybe just a little bit better than the worst. The typical choices of aluminum canoes or Old Town Discoveries are about the best most rental outfits will offer, and many places don’t even have boats that are that “good”. Renting will probably help you decide whether or not you will like having a canoe of your own, but you are very lucky indeed if you have the option nearby to rent something that’s even a little better than one that will at least get you on the water. If you have the option to rent better boats while deciding what you want, it’s a great idea.