Termium:

DEF – A method whereby certain libraries are entitled by
law to receive one or more copies of every book or other
publication which is printed or published in the country.
Source

CONT – Legal Deposit of new books 11.(1) Subject to
this section and the regulations, the publisher of a book
published in Canada shall, at his own expense and within
one week from the date of publication, send two copies of
the book to the National Librarian, who shall give to the
publisher a written receipt for the book. Source