I know this is late to the party, but the CA system in Canada was first implemented on 1 December 1972. As industry would not likely have caught up until their next batch of garments were created, it is safe to say most clothes bearing a CA number are from January 1973 onward.
Also on 1 December 1972, fabric content labelling became mandatory in Canada with The Textile Labelling Act and its complementary The Textile Labelling and Advertising Regulations, but there were exemptions: clothing made for religious orders, company uniforms, school uniforms, healthcare, and government agencies, if the clothing was made only for use within those institutions. This Regulations required labels to be bilingual. That said, many fabrics or yarns such as polyester is the same in English and French, so a label that says "100% polyester" is of no help. Look for other clues such as "Made in X/Fabrique en X".
However, care labelling was and continues to be voluntary. But if there are colored care symbols (red, yellow, green) on a label, that system was implemented in March 1970 (Standard for Care Labelling of Textiles). Initially, there was no mention of mandatory bilingualism because the care symbols were, well, symbols. However, the 1975 amendment allowed for additional written care instructions such as "hand wash only" or "dry clean only" and these had to be bilingual. There were several amendments over the years that further help to date vintage clothing made or sold in Canada (I've attached a history I wrote up). The use of colored care symbols ended in 2003 with the move to B&W symbols that integrated Canada and the US symbols following the 1992 Free Trade Agreement (why the integration took so long I don't know).
The Care Labelling Standard requires a permanently affixed care label or for the information to be printed directly onto the fabric. But the The Textile Labelling Act, however, allows for the manufacturer to print fabric content on a hang tag; the label need not be sewn into the clothing article. So while the presence of content and/or colored care labels helps to date an item to the 1970/1972 at the earliest, their absence is not definitive.