Hi Lokkabear--the currency used on
DCL is US. DCL is not equipped to do currency exchange. I believe there are no ATMs onboard ship.
Before we travel to the US (we live in Ontario), we purchase some US cash from a bank/credit union/currency exchange office. Shop around for the best deal. Try and get some small bills included in your US cash for incidentals and tips while travelling.
DH and I are old-fashioned, so we also buy US traveller's cheques from a bank/credit union/currency exchange, or from CAA (rules vary widely depending on your location--if you are a CAA member, check with your local office to find out if they sell them). If you do buy traveller's cheques, purchase them directly with Canadian funds so that you minimize bank charges.
Traveller's cheques can be difficult to use at stores, but I have never had any problem cashing them either at WDW or on DCL. Some hotels put a daily limit on the amount you can cash. You may have to produce a govt. picture i.d. to cash traveller's cheques.
You can also charge most of your US expenses on your credit card--your credit card company will charge you a currency exchange fee on each transaction. Prior to your trip, you should call your credit card issuers and advise them of your travel dates and itinerary, as credit card companies may flag/stop purchases made in foreign countries if the cc companies have not been previously advised about your travel.
If you decide to use a debit card, make sure with the card issuer that your card will work in ATMs in the US.