Discharging a Juror
Section 644 (1) and (2) states that:
Discharge of juror
644 (1) Where in the course of a trial the judge is satisfied that a juror should not, by reason of illness or other reasonable cause, continue to act, the judge may discharge the juror.
Trial may continue
(2) Where in the course of a trial a member of the jury dies or is discharged pursuant to subsection (1), the jury shall, unless the judge otherwise directs and if the number of jurors is not reduced below ten, be deemed to remain properly constituted for all purposes of the trial and the trial shall proceed and a verdict may be given accordingly.
R.S., 1985, c. C-46, s. 644; 1992, c. 41, s. 6; 1997, c. 18, s. 75.
A juror can be discharged where there is well-established information that a juror's impartiality is in questioned.
The judge will make inquiries to the alleged biased juror in open court. Counsel will be able to make submissions and suggest questions to be put to the juror.
A judge has the discretion to discharge a juror under s. 644 and continue the trial or can dismiss the jury and declare a mistrial.  The procedure requires the judge to:
- "apply the proper legal test for determining whether the information gives rise to a reasonable apprehension of bias”, and
- "at a minimum, conduct an inquiry into the circumstances in order to obtain the necessary information upon which to exercise his or her discretion" 
The decision to discharge is "highly discretionary" and so is afforded deference.
A judge generally should but need not consult with counsel before dismissing a juror.
Timing of Discharge
Jurors can be dismissed during deliberations.
Requests Must be On the Record
A judge may not hear requests and reasons for requests to be excused from members of the jury off the record and without the presence of the accused.
The jury can be reduced to as little as 10 members without a mistrial or a violation of s. 11(f) Charter rights.
It exists today in section 649:
Disclosure of jury proceedings
649. Every member of a jury, and every person providing technical, personal, interpretative or other support services to a juror with a physical disability, who, except for the purposes of
- (a) an investigation of an alleged offence under subsection 139(2) in relation to a juror, or
- (b) giving evidence in criminal proceedings in relation to such an offence,
discloses any information relating to the proceedings of the jury when it was absent from the courtroom that was not subsequently disclosed in open court is guilty of an offence punishable on summary conviction.
R.S., 1985, c. C-46, s. 649; 1998, c. 9, s. 7.
This rule, however, does not prevent the court from taking evidence from a third party or a juror about problems that may taint the verdict.
Once the jury gives a verdict the judge is functus and so cannot deal with any issues of irregularities in deliberation.
R v Budai, 2001 BCCA 349 (CanLII) at paras 27-40
R v Wolfe, 2005 BCCA 307 (CanLII) at para 5 (“When a juror’s conduct raises questions of possible bias, the trial judge may discharge the juror or dismiss the jury and declare a mistrial. Whether to take such a step is a matter which falls within the discretion of the trial judge....”)
- R v Chambers 1990 CanLII 47 (SCC),  2 SCR1293
- Budai at 39
- Budai at para 40
R v Li, 2012 ONCA 291 (CanLII) at paras. 77-8
R v Brost, 2017 ABCA 113 (CanLII) at para 7
Brost, ibid. at para 7
- R v Krieger,  A.J. No. 683 (C.A.)
R v Peters, 1999 BCCA 406 (CanLII), 137 CCC (3d) 26 (BCCA)
R v Kum, 2012 ONSC 1194 (CanLII)
- R v Sinclair, 2013 ONCA 64 (CanLII)
- R v Genest 1990 CanLII 3175 (QC CA), (1990), 61 CCC (3d) 251 (Que.C.A.)
- dating back to "Lord Mansfield's Rule" of 1785 which prohibits evidence of jury deliberation
- R v Pan, 2001 SCC 42 (CanLII)
see R v Lewis, 2012 ONSC 1074 (S.C.J.)
R v Mirza,  1 A.C. 1118
Standing Aside a Juror
633. The judge may direct a juror who has been called pursuant to subsection 631(3) or (3.1) to stand by for reasons of personal hardship or any other reasonable cause.
R.S., 1985, c. C-46, s. 633; R.S., 1985, c. 27 (1st Supp.), s. 185(F); 1992, c. 41, s. 2; 2001, c. 32, s. 40.
Calling persons who have stood by
641. (1) If a full jury and any alternate jurors have not been sworn and no cards remain to be drawn, the persons who have been directed to stand by shall be called again in the order in which their cards were drawn and shall be sworn, unless excused by the judge or challenged by the accused or the prosecutor.
Other persons becoming available
(2) If, before a person is sworn as a juror under subsection (1), other persons in the panel become available, the prosecutor may require the cards of those persons to be put into and drawn from the box in accordance with section 631, and those persons shall be challenged, directed to stand by, excused or sworn, as the case may be, before the persons who were originally directed to stand by are called again.
R.S., 1985, c. C-46, s. 641; 1992, c. 41, s. 3; 2001, c. 32, s. 41; 2002, c. 13, s. 55; 2011, c. 16, s. 10.
Discharging Surplus Jury Members
Trying of issues of indictment by jury
652.1 (1) After the charge to the jury, the jury shall retire to try the issues of the indictment.
Reduction of number of jurors to 12
(2) However, if there are more than 12 jurors remaining, the judge shall identify the 12 jurors who are to retire to consider the verdict by having the number of each juror written on a card that is of equal size, by causing the cards to be placed together in a box that is to be thoroughly shaken together and by drawing one card if 13 jurors remain or two cards if 14 jurors remain. The judge shall then discharge any juror whose number is drawn.
2011, c. 16, s. 13.