Welcome. I towed mine for 3 years with a 2003 Sienna, which is the generation before yours. You'll be ok, but even with the extra power yours has you'll feel the drag once you get above 50 mph. They aren't as aerodynamic as they look. All vehicles that are rated for 3500 pounds towing, like the Sienna, are really at their limits.
If you buy one, make sure you get a WDH (weight distribution hitch). The soft springs in all minivans are designed for 4-5 passengers and not towing. I towed for 2 years w/o a WDH and was so much happier - and safer - once I got it. I still use it with my current TV (tow vehicle) because it improves the ride quality. Many here have the E2 or Equalizer.