The class 3 hitch that John gave me mounts to a vehicle's frame through three holes on each side. The Sienna has three holes in the frame on each side. However it appears as though nearly every other dimension of the hitch will be mismatched, as hitches are not standardized and will be different for every vehicle. It is fairly easy to find vehicle specific hitches however, and they are relatively cheap ($150-$200).
The major manufacturers presently for hitches which fit my Sienna are Curt and Draw-Tite. This link is the money hit for chosing between them (oddly the Draw-tite wins on tounge weight and other specs by a lot):
https://www.etrailer.com/question-35975.html
It turns out that YouTube has tons of videos about how to install hitches on Siennas. What I learned is that if I had the plastic underbody cover the job would be twice as long, but since I don't have that then the weld nuts on my frame are essentially destroyed by corrosion and I'm going to have to spend a lot of time chasing their threads. Crazily the UHaul installation videos beat every other one out there hands down.
Here is one of many videos showing how agonizing doing the installation is with the plastic underside cover: https://m.youtube.com/watch?v=GTk8iqXha7Q
Here is the Uhaul vide for installing the Curt hitch: https://m.youtube.com/watch?v=cDU9Wo_MDGY&t=20s
Here is the UHaul installation of the Traw-Tite. The tool list shows the bushing pusher pliers that I will totally want to pop the tailpipe hanger off on the passenger's side: https://m.youtube.com/watch?v=Guz3s1FW7hA&t=18s
