Here is some thoughts on special purpose fundraising from the Ontario Public Guardian and Trustee.

Special Purpose Fundraising
Charities sometimes raise funds for a particular purpose or project and sometimes donors give money to charity for a special purpose. Donations received for a specific purpose or project and donor directed funds must be used only for the stated purpose and must be kept separate from the charity’s operating funds.
If a charity is fundraising for a specific purpose it is a good idea to provide an alternative purpose for which funds can be used.  That way, if the original purpose cannot be carried out or if there are surplus funds, the money can be used for an alternate project.

The alternative purpose should be communicated to potential donors when funds are solicited. If fundraising materials do not indicate an alternate use for special purpose funds, the charity will have to apply to the court to use the funds for a similar purpose or may be required to return unused funds to identifiable donors. Clear communication with donors during the fundraising campaign about all contingencies will help avoid problems. 
Charities conducting special purpose campaigns should retain the records concerning the fundraising campaign and in particular the information about what the public was told about how the money would be spent. Copies of fundraising brochures should be kept. The Public Guardian and Trustee may inquire into whether funds raised for a special purpose are being used for the purposes for which they were collected. Keeping good records helps to ensure that misunderstandings can be resolved quickly.