As far as I know the "tow prep package" on the Sienna didn't include either the hitch or the trailer light wiring. When I installed my hitch, I bought an aftermarket "plug and play" wiring harness for my 2013 that has a 4 pin connector. I bought both at: etrailer.com
Most 7-way harnesses I've seen or at least considered were set up to accept a connector from a 4-way harness. If you bought one of those types of 7-way harnesses, you would first install a 4-way harness and then plug the output connector from the 4-way into the 7-way harness. Then you run the additional 3 wires on the 7-way harness independently to power, brake controller and ground. There a lots of good plug-and-play 4-way harnesses. I've bought most of my trailer towing stuff from https://www.etrailer.com/ which has people who can make recommendations if you contact them.