Assuming that age is not a factor in the crime in the case, two offences come to mind:
- Sexual Assault (section 271 of the Criminal Code)
- Aggravated Sexual Assault (section 273 of the Criminal Code)
The primary question that you put forward is the question of consent. This is defined in section 273.1 of the Criminal Code:
Meaning of “consent”
273.1 (1) Subject to subsection (2) and subsection 265(3), consent means, for the purposes of sections 271, 272 and 273, the voluntary agreement of the complainant to engage in the sexual activity in question.
Where no consent obtained
(2) No consent is obtained, for the purposes of sections 271, 272 and 273, where
(a) the agreement is expressed by the words or conduct of a person other than the complainant;
(b) the complainant is incapable of consenting to the activity;
(c) the accused induces the complainant to engage in the activity by abusing a position of trust, power or authority;
(d) the complainant expresses, by words or conduct, a lack of agreement to engage in the activity; or
(e) the complainant, having consented to engage in sexual activity, expresses, by words or conduct, a lack of agreement to continue to engage in the activity.
Written consent is not the only form of consent accepted in a Canadian court of law. I would also expect such form to be rare. That being said, Section 273.1(2) communicates that consent is not valid if:
- A person other than the one engaging in the act provided the consent
- The person is incapable of providing consent. Such factors generally include age, mental or physical disabilities, or consent under duress (fear caused by another person)
- The person demonstrates by speech or conduct a removal of consent to engage in a sexual activity
The question of whether consent was obtained is something to be found in a court of law. You may have fun reading Section 276 which deals with disclosure and admissibility of evidence.