In the civil context, sexual assault is a form of battery: the intentional infliction of unlawful force on another.
The majority decision of the Supreme Court of Canada in Non-Marine Underwriters, Lloyd’s London v Scalera ,which considers the doctrinal dimensions of the tort of battery, is summarized succinctly by Allen M. Linden and Bruce Feldthusen, Canadian Tort Law, 10th Edition,
[Toronto: LexisNexis, 2014], beginning at para 2.32:

A person who proves that the defendant made direct physical contact with her person makes her case for battery. The onus then shifts to the defendant to establish that the contact was neither intentional nor negligent; or that the plaintiff consented to the contact or that a reasonable person would think she had consented. This nominate tort protects the interest in bodily security from interference by others. It is sometimes said that the contact must be harmful or offensive, but this is misleading. By definition, any contact beyond the trivial contact that is expected in the course of ordinary life is prima facie offensive if it is non-consensual. Every person ‘A body is inviolate. The tort protects the integrity of one ‘A person and does not require proof of further injury.

Two very significant evidentiary rules differentiate the determination of sexual assault in the criminal versus the civil context.

In a Civil Action the Burden to Prove Consent Rests with the Defendant

First, in a civil action, the claimant does not have to raise the issue of consent, disprove consent, or prove that there was no reasonable belief in consent (a concept not relevant to a civil claim). The evidentiary burden is to adduce evidence of consent; the legal burden to prove consent, on a balance of probabilities, lies with the defendant.

In a Civil Action the Standard of Proof is Proof on a Balance of Probabilities

There is only one civil standard of proof and that is proof on a balance of probabilities (even though the judge should be mindful of inherent probabilities or the seriousness of the allegations and consequences). In a civil action, the claimant need only prove the intentional application of force of a sexual nature to the one civil standard; that is, that it is more likely than not that intentional application of force of a sexual nature occurred. The claim is proven if the evidence is sufficiently clear, convincing and cogent to satisfy the balance of probability test.

These two rules are in sharp contrast to sexual assault in the criminal context where the evidentiary legal burden and standard of proof as to the intentional application of force of a sexual nature, and as to whether the claimant consented to that force, or whether the defendant knew or ought to have known that the claimant did not consent, remain throughout on the Crown and where the standard of proof is proof beyond a reasonable doubt, as described in R v Lifchus 1997 CanLII 319 (SCC) 1997, [1997], 3 SCR 320.