Yes, it is a crime to have sex with your spouse without their consent. In assessing whether or not an accused is guilty of sexual assault, a marriage between the accused and the complainant is not a viable defence.
Any sexual activity acted upon without consent is considered sexual assault according to the Canadian Criminal Code. In the context of marriage, if consent is not explicitly expressed, it is possible for a spouse to be charged with sexually assaulting their spouse.
The definition of sexual assault is very broad, illustrating what would constitute non-consensual sexual activity.
The definition of consent is found in sections 273(1) and (2) of the Criminal Code of Canada. The meaning of consent, subject to subsection (2) and subsection 265(3), consent for purposes of sections 271, 272 and 273 (the sections pertaining to sexual assault) means the voluntary agreement of the complainant to engage in the sexual activity in question.
No consent is obtained for the purposes of sections 271, 272 and 273 where an agreement is expressed by words or conduct of a person other than the complainant, the complainant is incapable of consenting to the activity, the accused counsels or incites the complainant to engage in sexual activity by abusing a position of trust, power or authority, the complainant expresses by words or conduct a lack of agreement to engage in the activity, or the complainant had consented to engage in the sexual activity, expresses, by words or conduct, a lack of agreement to continue to engage in the activity.
According to the Canadian Criminal Code, if convicted of a sexual assault, against your spouse, or any other individual you would be subject to sexual assault charges.
In particular, s. 271 which states that everyone who commits a sexual assault is guilty of an indictable offence and is liable to imprisonment for a term of not more than 10 years or, if the complainant is under the age of 16 years, to imprisonment for a term of not more than 14 years and a minimum punishment of imprisonment for a term of one year.
Alternatively, the accused can be charged with an offence punishable by summary conviction and is liable to imprisonment for a term of not more than 18 months or, if the complainant is under the age of 16 years, to imprisonment for a term of not more than two years less a day and to a minimum punishment of imprisonment for a term of six months.
A marriage between the complainant and the accused does not prove consent and is not necessarily a mitigating factor for the accused. However, it is possible for the defence to argue that the accused had an honest but mistaken reason to believe they had consent to engage in the sexual activity in question.
In any instance where a complainant reports that sexual activity occurred without their consent, the accused would most often be charged with sexual assault. There are viable defences available to you in the case that you are facing a sexual assault charge or any other criminal charge.