Yes, you will be seated with strangers on every attraction. They might be sitting beside you (every show), or the rows in front of you, or the rows behind you, but you will be seated with strangers. CM's count how many guests enter each show, with the expectation that every seat will be filled.
You'll also be expected to stand in every queue with strangers. Often they will bump into you, especially in preshow areas (Philarmagic).
Beyond that, if you take a bus, boat, or monorail; you will likely be seated touching strangers. Truly, far more than BTMRR, fellow bus/monorail travelers will often be seated close enough for body contact. Buses are filled to capacity- including all standing space. This includes all boat rides, llike Jungle Cruise. If you are standing on the bus, and the bus stops or turns, the person beside you will also lean into you. You will also be expected to sit/stand very close to strangers at every parade the fireworks. Last summer, a girl was so close to us, that her ice cream bar dripped all over us!
Also, if you arrive via MCO airport, the airport has a shuttle. It is very similar to the monorail, but usually less crowded. Still, when the monorail starts/stops, the person beside you may well lose their balance a little and bump into you. It's extra fun if they aren't wearing deodorant!
another time, I was seated on the bus so close to a fellow passenger that her sweat? (body fluid?) made my shorts damp, and her rough leg hair (stubble) prickled my legs. When she got up, a puddle remained. (at least I think it was sweat)
Then, if it has been raining, many passengers leave puddles on thier seats!