You can't. It's each merchant who integrates Bitpay. If they don't do it then you can't pay with BTC.

The closest alternative to Expedia available to pay with BTC will be lastminute.com as they sell hotels and flights.

You can buy gift cards for Bitcoin for it here - https://giftoff.com/gift-cards?filters%5Bsort%5D=alpha&filters%5Bcategory%5D=15&filters%5Bcountry%5D=80&page=1