Here is a note from CRA on cheque exchanges for Canadian registered charities.

Policy Commentary
Release Date
March 29, 2000
Reference Number
CPC – 017
Subject
Official donation receipts – Whether gifts of services qualify as charitable donations
Purpose
To clarify the Directorate’s policy regarding gifts of services.
Commentary
1. The Income Tax Act currently permits a registered charity to issue official donation receipts for income tax purposes for donations that legally qualify as gifts.
2. Contributions of services, that is, of time, skills or efforts, are not property, and therefore they do not qualify as gifts for purposes of issuing official donation receipts. Accordingly, a charity cannot issue an official donation receipt for services rendered free of charge.
3. A charity may issue an official donation receipt if a person provides a service to the charity, the charity pays for the service, and the person then returns the payment to the charity as a gift. In such circumstances, two transactions have taken place, the first being the provision of a service and the payment flowing therefrom, and the second being a gift proper.
4. The parties should be advised to proceed by way of an exchange of cheques. This ensures the presence of an audit trail, as the donor must account for the taxable income that would be realized either as remuneration (in which case the charity may also be required to issue a T4 slip) or as business income.
5. A charity should not issue an official donation receipt to a service-provider in exchange of an invoice marked “paid”. While this procedure does establish an audit trail, it raises questions as to whether in fact any payment has been transferred from the charity to the service-provider which in turn is being gifted back to the charity.
References
• Gifts and Official Donation Receipts, IT-110.
• Income Tax Technical News, Issue 26.