Generally speaking, a prepaid card should be accepted anywhere a Visa or Mastercard credit card is accepted.

However, there are situations where this may not be the case. Keep in mind that a merchant CAN choose to arbitrarily block all prepaid Visas/Mastercards. This often happens in situations where a credit card is used in lieu of a damage deposit, such as hotel bookings or car rentals.

Places that rent you a $20 000 car or a $50 000 room generally don't want to do so anonymously, they want to have a credit card they can charge for damages/cleaning/traffic tickets/etc after the fact, so they often don't accept prepaid cards. This is unfortunate, since many people without a credit card think they can just get one of the prepaid Mastercards or prepaid Visas and book a hotel or rent a car, but the reality is usually different. 

They may, however, accept prepaid "gift" cards as payment for a room or such, but will likely want something else as a damage deposit.

A company may accept the prepaid cards that have your name registered to them (or imprinted on it), but their policy may still be to not accept such cards. 

The BEST bet is to call the company in question and ASK!

In Canada? The best non-anonymous card is the BMO Travel Mosaik Prepaid Mastercard. The best pseudo-anonymous card is the RBC Prepaid Gift Card. I'm still on the lookout for a cheap completely anonymous Prepaid Mastercard or Prepaid Visa, but the Vanilla Prepaid Mastercard described here might be the best (scroll down!). Another option may be a secured credit card.