There are some of us who happily tow with a 3500# rated vehicle, so it's not an automatic "no". It's a literal YMMV. Do the homework, know what you're doing, know what you can do to maximize safety. Do what makes you comfortable. Have fun.
I can't speak to your particular vehicle, but for my sake, I did a TON of research on Sienna specific boards (SiennaChat and its predecessor) and found a whole slew of people who towed with the Sienna, TTs that were far more than a 2720 TM, and not one report of equipment failure or safety issues. So, I feel comfortable with what I am doing. BUT, I did the homework
I also weighed my rig, and do my best to keep the weight as low as possible, etc. I also only tow in the flat midwest. Things would be different if I were at altitude...
Welcome to the family!