Basically, all of UA's int'l flights departing from SFO leave from the int'l terminal. Makes sense.

Therefore, when your domestic flight to SFO ends up at the int'l terminal, you can probably figure the aircraft on which you flew will be going int'l for its next cycle.

If you need to make a connection at SFO, keep in mind there is a shuttle that runs between the int'l terminal and UA's domestic terminal so you avoid passing through security again.