The Charities Directorate of CRA cautions that official donation receipts cannot be issued for pledges.  When a person actually makes the donation then a receipt can be issued.

Here is the CRA summary policy:

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

“Pledges
Can a charity issue official donation receipts for pledges?
No. A pledge or promise to make a gift is not in itself a gift. Therefore, a registered charity cannot issue an official donation receipt for a pledge. However, when a donor honours a pledge, by making a voluntary transfer of property, a donation receipt can be issued.

Is a pledge enforceable?
No. Generally, a pledge does not constitute a contract, and is not enforceable.
References
• Registered Charities Newsletter No. 22 – Spring 2005
• CSP-P14, Pledges”