You'll find tax calculators here:
http://www.ato.gov.au/individuals/pathw ... 01_002_046
Here's a general tax chart that will help if you can't get the calculator to work:
http://www.ato.gov.au/individuals/conte ... fp=001/002
You can find information on your residency status here:
http://www.ato.gov.au/individuals/conte ... /64131.htm
I did a quick calculation and for $100,000 gross earnings you'd pay about $29,000 in tax. That's just a rough calculation and that's based on you being a resident for the full year (means you'd be a non-resident of Canada while you were away). Check out the notes on residency from the link above to figure out how it applies to your situation.
I should also note that you will need private health care here since you won't be covered under Medicare on a 457 temp visa. So if you can't get your employer to pay for it then you'll have to do it yourself, and that could be a couple grand per year.
What I would suggest if you are coming over here on a temp visa is that you ask your employer for living away from home allowance (LAFHA). It doesn't cost your employer anything, basically your employer pays part of your living expenses (rent, etc) directly from your pay. Then you get taxed on what's left of your pay, thereby reducing your gross income and also your tax. You wouldn't be able to buy any property though or you'd lost that benefit. Also, not all employers are willing to do this arrangement. Hopefully yours would because it reduces the amount of tax that you pay.
Also, see restrictions on the 457 visa and the notes on LAFHA at the bottom.
http://britishexpats.com/wiki/457_Visa_Restrictions