These acts could be sexual assault. Pregnancy is irrelevant to the analysis.
Deviating from the sexual activity consented to
A majority of the Supreme Court of Canada, in R. v. Kirkpatrick, 2022 SCC 33, in the context of a sexual assault charge, held that where birth control measures "change the physical act itself, like condom use" they are part of the "sexual activity in question" that is being consented to. Deviation from that activity is stepping outside of the consent.
For the majority, birth control measures can very well change the physical act and can be a condition of a complainant's consent. In Kirkpatrick the issue was condom use, but the language the majority used was "birth control measures." Whether birth control measures are in fact alter the physical act to which consent is granted in particular circumstances depends on the facts of the scenario. See para. 100.
What matters is whether the method of birth control changes the physical nature of the act (not whether the purpose was to prevent pregnancy) and whether consent was conditioned on that. So methods like diaphragms, condoms (penile and vaginal variants), and other barrier methods are all probably relevant.
Consent vitiated by fraud
There is an alternate path to sexual assault: if the consent was vitiated by "deceptions about the conditions or qualities of the physical act." See R. v. Hutchinson, 2014 SCC 19. Deceptions that deprive a person from the choice not to become pregnant, or exposing a person to an increased risk of becoming pregnant, or exposing a person to a significant risk of bodily harm such as a risk of contracting sexually transmitted diseases can all vitiate consent.
This path to sexual assault is not as straightforward as the path described above from Kirkpatrick, as it requires a showing of dishonesty, which can include non‑disclosure of important facts, and a risk of serious bodily harm (R. v. Cuerrier,  2 S.C.R. 371).
At least one court has said this reasoning does not apply when a person falsely represents that they are taking a birth control pill and then gets pregnant (PP v. DD, 2017 ONCA 180). This was in the context of a civil claim for sexual battery, but the court considered the reasoning from Cuerrier and found it was not analogous because the deceit had "no physically injurious consequences" for the plaintiff. The court recognized the consequences of a person having to support a child, but in the context of a wrong based on physical contact, what matters is physical damage.
the appellant's alleged damage is principally emotional harm or, in other words, hurt feelings and lost aspirations and/or career opportunities flowing from the birth of his child. His situation, as a man, is quite different from that of the woman. Clearly, there are profound physical and psychological effects on a mother undergoing a pregnancy that do not apply to the father of the child. The appellant was not exposed to any serious transmissible disease or other significant risk of serious bodily harm flowing from the intercourse. Moreover, it is noteworthy that the appellant was willing to assume some risk, albeit small, that pregnancy would result from the several instances of sexual intercourse, a risk present even where the woman is taking contraceptive pills.