The Toyota Highlander is built on the Toyota Tundra frame and uses the same running gear. However, at best the Tundra is a 7/8 scale truck, so it's not all that great. What you have is a truck or truck-based SUV.
If you had an RX330, you'd have a car-based SUV.
I think it is a unibody construction under there; I don't see a regular frame. The Four-runner is definitely a pickup truck chassis and a rear wheel drive basis. The Highlander is a front wheel drive like the Camry with extension to the rear wheels for the 4x4 effect. A true truck wouldn't have independent suspension all around.
If I'm not mistaken (which is possible) - the Highlander is actually built on the Camry platform. I think the Sequoia is on the Tundra platform...