The law regulating home based learning in Quebec is the Quebec Education Act.
Section 14 relates to compulsory attendance:
Every child resident in Québec shall attend school from the first day of the school calendar in the school year following that in which he attains 6 years of age until the last day of the school calendar in the school year in which he attains 16 years of age or at the end of which he obtains a diploma awarded by the Minister, whichever occurs first.
Section 15(4) relates to home based learning:
The following students are exempt from compulsory school attendance:
4) a student who receives home schooling and benefits from an educational experience which, according to an evaluation made by or for the school board, are equivalent to what is provided at school.
Section 18 relates to truancy and should not be applied to homelearners:
If a principal determines that a student is repeatedly absent without a valid excuse, the principal shall, after notifying the parents, report the matter to the Director of Youth Protection.
Although not required by law, it only makes sense that if you withdraw your child from school in order to homeschool, it is best to send the school a letter of intent so they know your child is not simply truant. If you have never registered your child in any school, such a letter is not necessary.
The Association of Christian Parent-Educators of Quebec has a helpful series of articles on how to interact with the authorities and protect your rights.
You can read the full text of the Education Act and other documents on the website of the Ministry of Education.