I'm not advocating towing anything over the rated load of your vehicle..... but unless you pull through a lot of steep hills or mountains, weight of a HTT is a distant second to the heigh/size/wind resistance. You will have a much better time towing a heavier, sleeker trailer, than a blocky light one.
Our sunset trails 17' is like towing a parachute, for a light trailer, it doesn't tow like one. I'm not sure I would tow a hybrid your vehicle. What year and powertrain is it? The only highlander info I find with a tow pack is 5000lbs?