Yes, you're still eligible to sponsor him. As a Canadian citizen you can apply to sponsor him while you're still living in Australia, however you will have to include proof of your intent to re-settle in Canada - a job offer, lease (mortgage) agreement, etc. There is no minimum income requirement for spousal sponsorships, so the fact that you've been working in Australia won't matter.
The best (and really only) option for applying is via
the outland process - that simply means that the application will be processed at the visa office that represents his country of birth rather than being processed entirely within Canada. That would only be an option if you were all in Canada now - and it's really not in your best interest anyway for various reasons. First of all, inland has no right of appeal, and secondly, it takes 12-18 months to finalize.
Your husband's application will be processed through Sydney - they are currently finalizing spousal aps in 3-8 months, plus it'll be about a month for the sponsorship approval through the Case Processing Centre in Mississauga when you first submit the application. So, now is about the time to start getting prepared for a move next summer - it should give you time to get things finalized before you need to worry about coming to Canada. Then, once his application is approved, you come together to Canada and you don't have to worry about separation.