Static load (load not moving): I would say it probably could hold more than 110 lbs.
Dynamic load (load is moving): I would say do not go over 110 lbs.
Now you say, "The load won't be moving because I will have it strapped down/attached to the roof rack." There in lies the fatal flaw. Your load will be moving and depending on the bumpiness of the road, or one good dip in the road, that 110 lbs can GREATLY increase. The roof rack is not connected to your frame so there is some flex in the cross members. If the load is too much and a dynamic force (going over a dip) is exerted on the crossmembers......snap!
Try this; take a paper towel and place a full soda can on it. Now gently and slowly lift the paper towel up so that the paper towel holds the weight of the can. Now give the paper towel a fast little up and down motion, like a car going over a dip or bump. What happened? Same thing with the roof rack. Depending on the quality of your paper towel, you may need to get it a little wet.
How heavy is the canoe? Just because the ends are tied to the bumper/frame that doesn't mean the downward load/force (i.e. weight) is transmitted to the bumper/frame. The only thing the tie-straps, rope, bungee, etc. are doing is preventing the canoe from sliding off or bouncing up. The roof rack is still supporting the load. If you don't believe me, try lifting the canoe by pushing up on the tie-straps, rope, bungee, etc.
I think the proper solution is to make a variety of racks (perhaps modular) that fit into the bed extender brackets. I was tempted to start my own company to do just that. But I'm too lazy so far to start my own company.
If your RL is equipped with a hitch, can't you attach some type of extender off the hitch which will help distribute the weight? In the example of the canoe, put one end on the roof rack and the other on the hitch extender. Any thoughts?