Here is a Receipting Kit for Canadian Registered Charities that I prepared. The kit is 174 pages long and provides an overview of what a registered charity needs to generally know about receipting as well CRA guidance on receipting and even a CRA auditor checklist on receipting.
Here are some other resources for Canadian registered charities on issuing official donation receipts:
Do you require legal advice with respect to Canadian or Ontario non-profits or charities?
Mark Blumberg is a partner at the law firm of Blumberg Segal LLP in Toronto and works almost exclusively in the areas of non-profit and charity law.