Wonka,
Visa USA and the MC association handles all the forex transactions. They charge their member banks 1% of the total amout, but they use wholesale exchange rates. Most banks and credit unions pass on that 1% charge to their customers. It will show up as a separate line item on your bill. A few, like Cap One, don't charge any additional fees and don't even pass through the 1% charge. Passing on the 1% charge is fair. Not passing it on is a bargain.
Several issuers, like Chase for example, add additional junk fees to forex transactions, which can be as much as an additional 3% fee. You should avoid using those cards overseas. But even if you can't, 3% over the wholesale exchange rate is not a bad exchange rate. It's just that you're paying a little extra when you don't have to. Amex typically charges 2% forex fees (total), but it's hard to figure their exchange rates. Still a good deal though compared to changing money overseas for most of us mortals except Carolinian who lives in Eastern Europe and knows this stuff like the back of his hand.
Apply online, you should be able to get a card before you leave. It might not matter for charges made on board. They might just show up as dollar denominated US charges. It will matter for charges you make at the ports of call, but it doesn't really matter all that much in the grand scheme of things.
For the rest of it, you're just going to have to do your own research to see which rewards cards work best for you. bankrate.com is a good place to start. It really depends on your spending patterns, where you have miles/points, which programs you are or want to be invested in, etc, etc.
-David