1.26.15 | Reddit
Canadian sexual assault law has already interpreted s.273.1 of the Criminal Code (the concerning 'consent' in the context of sexual assault) as essentially requiring affirmative consent: R v Ewanchuk  SCC.
In terms of the act of sexual itself, 'consent' is defined as the private, subjective state of mind of the complainant - whether or not they communicate it in any form. For the corresponding mental element of the crime, 'consent' is defined as the accused knowing of, or being reckless or wilfully blind to, the complainant's lack of affirmative communication of consent. Prior to Ewanchuk, the mental element was simply knowing of, or being reckless or wilfully blind to, a lack of consent. Post Ewanchuk, the threshold was lowered in favour of the complainant: now, the accused need not in fact have to have (some level of) knowledge of lack of consent, but merely (some level of) knowledge of a lack of affirmative communication of consent. This is an important difference, and everyone in Canada should be aware of it. Now, before going on...
Note: none of the above or below constitutes legal advice of any sort, and no rights or obligations are created therefrom. For legal advice, contact a lawyer. I am not your legal representative in any way, shape, or form
So, in Canada, we really do have affirmative consent in place. However, one difference: consent, under Ewanchuk, can be 'affirmatively communicated' by either verbal language or body language (or both, of course).
Note, however, that if the 'affirmative consent' movement seeks to take this further, by requiring overt verbal expression of consent, nothing would be gained. The fact is, unless each party to a sexual encounter were literally saying 'I consent' non-stop, throughout the encounter, a verbal expression of consent beforehand would still not be sufficient to prevent against the possibility of a sexual assault (to either party) - because consent must be ongoing, and can be revoked at any time (recall again the distinction above: 'consent' is defined differently as it relates to the act, and the corresponding culpable mental state, of the crime). Without the legal availability to draw from body language in order to determine consent to sexual activity, either prior to initiation or throughout, human sexual relations would become a minefield of legal liability. This is not to say that false accusations of sexual assault would be any more prevalent than they are today (and I do not here make any claims at all about this prevalence or lack thereof). However, legal liability - the bare exposure to potential criminal punishment - would in fact dramatically increase.