The recent dip (nose dive?) in the value of the Cdn dollar is precisely why we opened our US $ savings account. We were really lucky that we deposited money into it, and paid off our package back when the dollar was sitting pretty at $1.05. We saw that the dollar had started to slip just before we left for our vacation and made the decision to bring cash with us instead of using our credit cards.
Yes, I know lots of people are afraid of carrying large amounts of cash with them, but it works for us. And we avoided currency conversion fees from the credit card company as well as further erosion of the dollar value during our trip. As long as you're prudent. We carried most of the cash and our passports in our money belts, with only enough cash for each day in our wallets. We did have a couple of credit cards in case of emergency, but never used them. Once we got to WDW, the credit cards and most of the cash went into the room safe. We charged all of our purchases onto our KTTW and paid it off in cash as well.
Even driving to and from the world was easy when paying cash. Several times (especially when paying for gas) we got discounts for not paying with a credit card.
Now I realize that many people will balk at the idea of carrying real money around, and it won't be economical unless you can buy that cash at an excellent exchange rate. We got lucky this time, and hopefully will be able to make a timely currency purchase before our next American vacation.