Quote:6.1
Official First Day Covers
Customers wishing to have their own first day cover cancelled are to forward the self-addressed cover to the National Philatelic Centre in Antigonish.
NATIONAL PHILATELIC CENTRE
Canada Post75 ST NINIAN ST
ANTIGONISH NS B2G 2R8
The cover is to be mailed early enough to arrive at the destination for the first day of sale of the new stamp. A charge per cover is levied for stamp affixing, cancellation and return through the regular mail service.
Cancellation of first day covers is available free of charge to customers who take their cover to a post office.
On request, philatelists may obtain a clear cancellation of philatelic covers by taking them to a post office and handing them in with a second envelope bearing a complete and valid postal address and sufficient postage to enable such mail items to be forwarded to the addressee through regular mail delivery channels.
Such requests received by a postmaster for cancellation and reposting will be complied with only if the volume of the covers does not disrupt regular postal services.
This does not sound like you get a grace period like here in the US.
For clarification, the phone number for "Philatelic Customer Service" is 1-800-565-4362 (from Canada and the United States).