Freighter Problem
I think CX are trying to "plug the dyke" short term by offering a Sydney roster for -400 guys. This is a short term roster to crew the freighter on passenger pay. Of course the shortage is not a Sydney base problem as such - its a Freighter wide shortage, so while your family might be based in Sydney for a few months, you will more than likely be spending most of your time disrupted around North America !
They are also drafting alot of airbus pilots onto the -400 right now. The assumption is I think that many of them might also crew the -400 freighter, as alot of the existing -400 crew have removed their names from the freighter operators list.
The history behind the current freighter problem is from when they employed alot of North American furloughed pilots. CX made them resign from their previous positions, but under the furlough rules no resignations are recognised. These chaps are now steadily being offered their old positions back in order of seniority. CX freighters is the lowest paying North American -400 operator, so its difficult to attract new pilots beyond the short term. There are always those who come for a type rating and the typical 1000 hours on type. So, the current pilots are leaving, fewer new pilots are joining, and the passenger pilots don't want to crew the freighter either. (Well, some do, there are always those who don't see the big picture)
This might finally be time for CX to raise the freighter pay scales if the supply/demand forces prevail.