You would want to look into what Toyota includes in the tow package, and add as much of that stuff as you reasonably can. Especially if the package had more cooling for the tranny. That is important for your vehicle's longevity.
Once you have it appropriately equipped, the Sienna should be a good tow vehicle. The same 3.5L is in my Highlander, and it gets a 5000 lb tow rating in the HL. Scamp
16's tend to not be overly heavy on the tongue, so that will count in your favor with the Sienna's rear suspension. I would suggest an Andersen No-Sway hitch with that rig, as a few Scamp 16 owners have reported some sway-ish movements... perhaps due to the tongue being relatively light
as it is.