Check Your UA Itineraries for Schedule Changes and what to do after one
#317
FlyerTalk Evangelist
Join Date: Aug 2005
Location: BOS/EAP
Programs: UA 1K, MR LTT, HH Dia, Amex Plat
Posts: 31,837
They will get you on the next available UA flight from SYD, they may also look for SYD-(BNE/MEL/AKL/CHC)-SFO options. If this is a paid ticket & with some persistence you can probably get them to re-route you on QF, assuming there are no seats on UA metal flights available.
UA will also pay hotels/meals as appropriate assuming the cancellation is 'controllable' (which most of them are on this route).