Bill C-38: The Civil Marriage Act
...codifies a definition of marriage for the first time in Canadian law, expanding on the traditional common-law understanding of civil marriage as an exclusively heterosexual institution. It defines civil marriage as "the lawful union of two persons to the exclusion of all others" thus extending civil marriage to conjugal couples of the same sex.
I was thinking it could be considered illiberal because in section 15 of the Charter of Rights and Freedoms it talks about laws being enacted without discrimination, but this act is without discrimination on the basis of sexual orientation. So its discriminating on a certain group, but I am not totally sure that is the reason.