It is very difficult to use your Continental miles to upgrade international flights, and CO itself only flies to Cairns anyway (from JAX, via IAH, HNL and GUM).

If you are set on flying to Sydney your best choices are Qantas or Air New Zealand via LAX; UA via LAX or SFO; or HA via any west coast gateway, and then HNL. (You can also take any number of Asian carriers like CX, JL or KE, changing in some Asian city, but it'll take you waaaay out of your way.)

If you had 105,000 CO OnePass points, that would be good for one business-class ticket to SYD on QF (availability is no sure thing, though, and if you're catching a cruise you probably don't have much flexibility on flight dates).

Upgrading is easier on UA but Amex points don't count for anything with them. The only way I think your Amex account balance might help would be if you wanted to try flying Hawaiian Airlines, say, LAX-HNL-SYD. You can buy Amex points at $25 per 1000, topping up your current balance until you had enough for two business class tickets, and simultaneously transferring the lot into Hawaiian's FF program. If you've already got 100,000 Amex points, another 100,000 points would be $2500 -- not unreasonable for two premium seats down to Oz. You would still have to get from JAX to LAX on your own dime though.

Your best bet, if you are willing to spend a little money to travel in business class, might be to hang into your miles and points and book through a west-coast consolidator offering cheap premium-cabin fares, which often come up on second-tier Asian carriers like Korean Air or Thai.

Good luck...