Brady v. Maryland, 373 U.S. 83 (1963) holds that withholding exculpatory evidence violates due process "where the evidence is material either to guilt or to punishment". This is similar but arguably more limited than the Canadian position. In Canada all material evidence (subject to privilege) held by the prosecution must be disclosed.
In America request for disclosure is (usually) required.
A defendant's request for "Brady disclosure" requires the prosecution to disclose material exculpatory evidence to the defense. Exculpatory evidence is "material" if "there is a reasonable probability that his conviction or sentence would have been different had these materials been disclosed." Brady evidence includes statements of witnesses or physical evidence that conflicts with the prosecution's witnesses, and evidence that could allow the defense to impeach the credibility of a prosecution witness.
Because of the Brady ruling, prosecutors are required to notify defendants and their attorneys whenever a law enforcement official involved in their case has a sustained record for knowingly lying in an official capacity. In Canada evidence of police misconduct is also producible and the Crown must make inquiry to obtain such material. Brady evidence also includes evidence material to credibility of a civilian witness, such as evidence of false statements by the witness or evidence that a witness was paid to act as an informant.