Sometimes prepaid cards have issues with online purchases because certain payment processors attempt to do validation using the cardholders address. The most common prepaid cards that I see at places like Superstore and other grocery stores are "Vanilla Mastercards". Reading online, they may require you to register a postal code with Vanilla so that the validation stage will succeed.
I'd say that chances are they will work, maybe do a bit of research online with the specific card distributor and what they suggest for online purchases.