Can't Miss Restaurants in Australia

if you are visiting the center of Melbourne, its worth knowing that Melbourne is known for its 'trendy' cafes and bars etc along narrowish lanes not far from the main flinders st train station.
https://www.timeout.com/melbourne/restaurants/the-best-flinders-lane-restaurants

In Sydney , definitely somewhere on the harbour, there are plenty of options near the opera house/circular quay/the rocks/darling harbour. if you want to keep in the action.
but if you are after views there are are places like a revolving restaurant on the top of australia square ( O bar)
https://www.timeout.com/sydney/restaurants-cafes

In Adelaide ( not that I have been there yet) but I would pick somewhere in the barrosa valley
http://www.barossa.com/

Australia is fortunate to have some of the best produce and chiefs in the world, so you shouldn't have any problem finding places to eat. prices are generally moderate, from what we have found ( compared to europe)

hope this helps.

linda, when you are in Sydney you will need to look into buying an opal card, for transport. (like the oyster card in London) makes it so easy to get around.
https://www.opal.com.au/en/about-opal/opal_for_visitors/
http://www.sydney.com/

there are plenty of things to see and do in Sydney ( at the moment there is VIVID - where they light up the city) http://www.sydney.com/destinations/sydney/sydney-city/vivid-sydney

you may consider touring through and eating at the opera house?
http://www.sydneyoperahouse.com/visit/tours.aspx

if you are thinking of climbing the bridge ( which is great BTW), remember you can always just walk over it at roadway level, for free, for good views. its impressive in size. built about the same time as the golden gate bridge, but much wider and 'substantial' IMO.

We've always relied on TripAdvisor to start our restaurant search wherever we've been. The map feature can help narrow down choices to specific neighborhoods ...in The Rocks for example, where there are a ton of great options including the Fortune of War, which I think advertises itself as the oldest pub in Oz...looks like it anyway.
For a unique lunch experience you might consider catching one of the mid day ferries over to Doyle's at Watson's Bay. It's something of a Sydney institution - a bit pricey but quite good. There's a nice coastal walk there if you want to walk off your lunch after, with some pretty, distant views down the harbor to the Opera House and Harbor Bridge.
Good advice re the Opal card...

We, too, use Trip Advisor, but not solely. One of our very best meals in Australia was eating the picnic supplies we had picked up at Maggie Beer's (in the Barossa) at the cottage we were staying at along with a great bottle of wine. I can still remember that, although I can't remember a single restaurant. Restaurants do change and come and go.

We also wandered into a pub in Adelaide, and ended up going there 3 times - good beer. Nothing special, but the staff was very friendly and the beer was tasty. Suggest you just wander into something and see if you like it. Those unexpected finds are the joy of travel. And the Central Market in Adelaide is amazing. Lots of takeaway, amazing food and produce, picnic supplies, etc. We could have eaten out of there for a week.

We ate well in Melbourne a few years ago, and it does have a great restaurant scene (which probably changes all the time).

Ask your hotel, taxi driver, or the local winery you are visiting. Especially, the wineries, they probably won't steer you wrong.

Have a great trip! Maybe Judy will chime in with her suggestions.

The Barossa Valley is great but a bit of a drive from Adelaide if you are thinking about dinner. You might enjoy Red Ochre Grill in Adelaide for modern Australian cuisine using native ingredients. In the city centre there are lots of choices reflecting Adelaide's multicultural population favourites of mine include The Greek on Halifax, Amalfi Pizzeria Ristorante (has great Italian dishes as well as pizzas) and Madame Hanoi (described as French-Vietnamese fusion). In Port Doulglas we enjoy the casual Australian atmosphere of the pubs in McCrossan St. For water-side dining without a hefty price tag the Tin Shed restaurant at the combined services club is very good, we like to get there late afternoon to have pre-dinner drinks while watching the tour boats returning to the Port from the reef. Both Adelaide and Port Douglas have lots of choices that would cater for most tastes and budgets and provide memorable dining experiences. Have a great trip.

When we were in Australia in 2013 there was a chain of small restaurants called Pie Face. We loved this place. They had small breakfast pies with eggs, cheese and bacon as well as for lunch pies with great choices.

We found Sydney restaurants to be very expensive, much more than in our 1998 visit. So we skipped the seafood places in the Rocks and on the Harbour and opted for a small Japanese place instead. But we did splurge for lunch on a daytrip over to Manly and ate at the Manly Fish Cafe, sitting outside ( no view of the water). The fish was terrific---I had the Barrimundi.

re dining in Adelaide. You will be spoilt for great choices. The Barossa Valley has some wonderful restuarants. Fairly long way to go just to dine. If you are staying a day or two I would recommend Hentley Farm or Fino at Seppeltsfield. If you are going as far as the Clare Valley, one of of my all time favourite places is Skillogalee Winery. However, you would definitely need to stay overnight to enjoy this experience.
In Adelaide and surrounds, I would recomend Windy Point Restuarant for dinner. The food and night view are both spectacular. Also love The River Cafe for either lunch or dinner. It is situated on the edge of the River Torrens.
Enjoy