DH and I always carry travellers' cheques. When we go to the U.S., we purchase the cheques in U.S. $ in Canada. We shop for the best rate, which is CAA for us. We try to bring as much as we think we will use, and an emergency supply. We also carry U.S. currency. We do not exchange our unspent travellers' cheques back into Canadian currency--we either cash all the cheques in the U.S., or just cash some. Unspent travellers' cheques (like U.S. currency) can be held until the next time you need it.
Our system may not work for everyone, but we visit the U.S. at least once a year, and it is just not worth it to us to pay bank fees for changing money back and forth, especially with interest rates so low and fees so high. We used to have a U.S. bank account with Desjardins Credit Union, but they piled on so many bank fees, we closed the account.
We never have any trouble cashing our travellers' cheques at WDW. We usually cash them at our hotel (either onsite or offsite). There is usually a limit on how much you can cash per day--often around $200.