Hi dianewb,
I book hotels with my Bank of Montreal Prepaid Mastercard. No one has ever questioned it.
As for getting a secured credit card while paying a proposal, I contacted People's Trust (they offer a secured Mastercard) myself to ask about this, and the representative emailed back to say that they do provide cards to people who are still paying off proposals - you just have to wait a few months after starting your proposal so that it shows on your credit report that your previous debts are covered under the proposal.
I have recently applied for a HomeTrust secured VISA card to begin rebuilding my credit rating. I will post here again to let you know if the application goes through, but the HomeTrust VISA is recommended for people in proposals.
The individual you talked to at your bank may have limited information, and your particular bank may be conservative. Don't give up - you can get a Bank of Montreal Prepaid Mastercard, or a secured credit card, and book hotels with it.

Best wishes,
~Wendy