Sunstate and Eastern are 2 different companies both with separate EBAs. If you want to work in QLD you are on the Sunstate EBA. For WA, NSW and VIC you are on the Eastern EBA. Both EBAs have all types covered at a similar pay level (Within a few hundred $ of each other). In recent years the two groups have come closer in terms and conditions rather than apart. However there are still a few small differences.
Previously Sunstate was the only company to have Q400s on its EBA and as such they opened a Canberra base on the Sunstate EBA to fly Q400s between Canberra and Sydney. A short while later Eastern had the Q400 put on their EBA, this made the Canberra base redundant and it was closed with the flying done out of Sydney by Eastern Crew.
From a pilot perspective the only real issue with having the two separate companies is that if you want to transfer to the other one you loose all your seniority as they each have their own seniority lists.