Thank you for the questions.
Unlike some countries, Canada does not have a single statute that codifies all of the federal aspects of marriage, marriage of course being divided constitutionally between the federal parliament that has jurisdiction over the legal capacity to marry or who can marry who and the provinces and territories that have capacity over the solemnization of marriage, licensing, registration, and other things like that.
The Civil Marriage Act, when it was first passed, was passed for a particular purpose, and that was to provide equal access to civil marriage to same-sex partners. Over time the Civil Marriage Act is becoming a codification of all of the federal aspects of marriage. The amendment would add two aspects, which are currently only within the law for the province of Quebec. The statement that you must give free and enlightened consent exists in the common law, so it's very clear in the rest of Canada but it is not in a statute anywhere that you can point to.
Having it in a statute you can point to will make it somewhat easier, as the U.K. experience has shown. Having a statute in the United Kingdom that says you can't force a child into marriage has allowed children there to say to their parents, “Look, it's in the law that you can't do this to me”. In the same way, this will provide that for children in Canada.