Here is CRA comments on whether a Canadian registered charity can return a gift to a donor?

http://www.cra-arc.gc.ca/chrts-gvng/chrts/prtng/gfts/rtrnng-eng.html

“Returning a gift to a donor
Can a registered charity return a gift to a donor?

In most cases, a registered charity cannot return a donor’s gift. At law, a gift transfers ownership of the money or other gifted property from the donor to the charity. Once the transfer is made, the charity is obliged to use the gift in carrying out its charitable purposes.

However, a charity may try to retain the goodwill of donors seeking the return of their gifts by offering to transfer the gifted property to another registered charity.

When a registered charity must return gifts to donors:

A charity is occasionally obliged by law to return gifts to donors. This can happen, for instance, when a charity asks the public to contribute to a special project and later events make it impossible to carry out the project. Under certain laws, ownership of the gifted property can revert to the donors if the project becomes impossible to fulfill.

The return of gifts to donors falls more appropriately under trust law than the Income Tax Act and is ultimately a matter for a court to decide. A charity may wish to consult legal counsel in these instances. We also strongly suggest that the charity, or its legal counsel contact the Charities Directorate if it appears that the charity may have to return gifts to donors.

How to avoid having to return gifts to donors:

When a charity is seeking funds for a special project, we recommend that the charity clearly inform donors, and/or state in its fundraising material, before accepting any donations, what it will do with the money if the project cannot be carried out or if more money is collected than the project requires. The charity could state, for example, that it will apply any unused donations to its other programs.
References
• CSP-G04, Gift (Conditional)