So here's an update on what I'm looking at as the two safest options (for making connections or recovering from misconnects):

SAN-ORD-YUL, dep 0845, arr ORD 1432, dep 1545.
and either LX: YUL-ZRH-CDG (60min connect in ZRH, longhaul equip: 332)
or AC: YUL-YYZ-CDG (100min connect in YYZ, longhaul equip: 763)

Actual flight mileage MEL-SYD-LAX/SAN-ORD-YUL-ZRH-CDG-SIN-MEL seems to be 24839, but on MileagePlus I should earn 500 on MEL-SYD (UA), and 500 on either YUL-YYZ (AC) or ZRH-CDG (LX) which would then bump me over 25000, right?
(25112 via YYZ or 25098 via ZRH)

I feel guilty for not maxing out the 26k limit on this fare, but the schedule looks too tight. Forgive me for lack of aspiration