will probably weigh in at ~4,500 lbs when you have some stuff in it. You should avoid carrying water in the tanks as that will push the trailer weight up closer to the max 5,000 lbs.
The tongue weight is where you will run into problems. This trailer will most likely be in the 650 to 700 lbs range when ready to travel.
That is what you need to determine from Toyota is the hitch weight (tongue weight) capacity of the Sienna.
Also, this will come off your available cargo capacity so for example, if the cargo capacity is 1,500 lbs and 700 goes to the trailer. That doesn't leave much room for people and items in the Sienna. Add the weight of a weight distribution hitch to your cargo number
There are a few towing calculators online, try searching for one of these and enter your numbers in there along with the Airstream numbers.
Keep in mind that the published tongue weight from Airstream is usually low.
If you are set on the Caravel, perhaps a slightly older unit would be lighter. Or have a look at the Sport 22FB which is lighter and narrower but less feature rich.
Once you get a good match, I am sure you will have lots of great adventures with your rig!