You have a couple of options: both need to be done BEFORE your current temporary status expires, and you should always track any shipment to CIC for proof of delivery. Your first option is to include an
application to extend your stay/change your conditions WITH an
inland PR application. You should check "initial work permit" on the extension application form, include the $150 fee, and that will give you "implied status" to remain in Canada legally until your PR application reaches first stage approval (which, under normal circumstances, takes about 6-7 months). If you do that, when you reach AIP you will automatically be issued a new temporary status document (open work permit) that should last you until processing is complete (another 6-12 months). The two principle drawbacks to inland aps are that they have no right of appeal and you are basically stuck in Canada until they're finalized because you have to be resident in Canada, with your sponsor, in order to be approved. If you leave Canada and are not able to re-enter, that application is forfeited.
You could also elect to file an
outland application - that doesn't give you the work permit option, but you'd still file (separately from the PR application) to extend your status using the same application linked to above and as long as you got the application to them before your current status expires, you'd have "implied status" to stay in Canada until they make a decision on the extension (about 75 days). All you'll need is proof of your legal marriage, proof that you have a PR ap in process, and proof that your sponsor has funds to support you, as well as the other info they request in the application's document checklist. An outland application has the right of appeal, there is no residency requirement (either in Canada or in your home country), and outland aps are usually finalized much faster than inland aps. After the six week sponsorship assessment at the Case Processing Centre in Mississauga, your file would be transferred to Sydney for processing (assuming your sponsor was approved). Sydney is currently finalizing spousal PR aps in 3-7 months. The priniciple drawback to an overseas (or outland) application is that, IF an interview is required, you have to attend at the overseas office. But if you provide sufficient documentation of your relationship, spousal applicant interviews are often waived. You also have to get your passport to the overseas office at the end of the process to receive your Confirmation of Permanent Residence, which you take to a Canadian port of entry to "land" . . . so if you can't mail your passport back to Australia, that might be something you don't want to have to deal with.
Only you can decide how important the right to appeal a refusal is to you - and whether a longer processing timeline (with the option of a work permit) is preferable to having things done faster, but only being able to stay as a visitor.