I am flying YYZ to SYD in a couple of weeks. I do not travel too often but certainly want to pick up the points to put towards a flight, probably in North America. Would Onepass be the right program for me. My home airport is Toronto. Any idea how many points this trip would accumulate?

I assume you are flying a QF (Qantas) flight from LAX-SYD, with a connecting flight from YYZ-SYD. (Otherwise, on AC or UA, you won't earn any Onepass miles.) If that connecting flight is on a QF code, it will be operated by AA, which means you won't earn any Onepass miles for it. Therefore on Onepass you'll earn miles only for LAX-SYD-LAX, a total of just under 15000 miles. This applies if your QF fare is in booking codes B, G, H, K, L, M, N, O, Q, S, T, V, W, or Y, which covers pretty much all coach fares.

If your flight is a cheap fare on QF, your only real alternatives are AA, QF, and AS. On AA, you'd only earn 50% miles in M, V, L, R, G, O, and S class, and nothing in Q. You might get 100% mileage on the connecting AA flights, in which case you'd get just over 11000 AA miles. If your QF flight is in Q, one of the cheapest fare classes, you'd get nothing on AA.

Another alternative is to put the miles in a QF account. These can be used for awards in North America on AA or US Airways; you'd earn over 19300 QF points, but QF points are not nearly as valuable as AA or CO miles except for a few specific uses like one-way awards.

Last, you might want to go with Alaska Airlines. I believe you would also get 100% mileage in all coach fare codes on both AA and QF flights, so you'd end up with 19300 AS miles. Since AS has a lot of partners, you should find it easy to earn another 5700 miles to get a North American domestic award ticket. I think this is your best option all things considered, unless you already have some AA, CO, or QF miles.