The presumption of innocence sets the criminal trial's default: the accused starts innocent in law and remains so unless the prosecution proves every element of the offence beyond a reasonable doubt. The accused may test the Crown's case and call no evidence at all; silence is not guilt.
The presumption reaches beyond the verdict — it shapes bail (detention before trial is the exception), reverse-onus provisions (suspect, because they convict on doubt), and the rule that an acquittal is not a finding of innocence but a finding that guilt was not proved. The system prefers acquitting the guilty to convicting the innocent, and says so openly.
Section 11(d) of the Charter guarantees the presumption expressly, and the leading case on justifying limits on rights — R v Oakes — was itself about a reverse-onus provision that presumed guilt.