Euros and UDS $ and Canadian Dollars are accepted all over in Turkey.
Museums only do accept YTL (Turkish Liras) but credit card can be used.
There are ATM s all over if you need YTL.
Euros and US Dollars or main credit cards can always be used for mid to large purchases but you will need a small amount of Turkish Lira for entrance fees, small souvenirs, a bottle of water and the like. You can just change some at an ATM on the day easily.