I don't know about overseas employment tax credits, but have been told that if you are in Oz for a temporary stay (you haven't been accepted for permanent residence) that the CRA doesn't look at your earnings there and the Ozzie tax people don't look at your earnings in Canada
if you have been declared a non-resident of Canada.
You need to look at the CRA website - search cra and expat and it will lead you to the NR-73 form. Submit this form and they'll tell you if you would be considered a non-resident. It's pretty tricky depending on if you own real estate here or if your partner isn't moving with you. You can also call the CRA help line at 1-800-959-8281.
If you go the non-resident route you need to notify all of your financial institutions of the date you become a non-resident (generally your
flight date)because they will have to withhold taxes on your interest, dividends, ect. so you will not have to file returns for the tax years you are in Oz. The first year you leave, you will have to file returns in both Oz and Canada.
We're lucky, the company sponsoring us is paying for PriceWaterhouseCoopers to do our taxes the year we leave, so I don't know how much they charge but they have been very informative. Don't forget, you can call the CRA and they will explain things to you if you know the right questions to ask. There's also a whole bunch of stuff you'll need to know if you have mutual funds and/or stocks because their value will have to be assessed for your departure date for capital gains, but I really don't know that stuff.