While the result of a trial may be a foregone conclusion after an unsuccessful Charter motion to exclude evidence, an accused must still decide whether to change his plea to guilty, or to maintain his not guilty plea and have the judge make a finding of guilt.
If an accused wants to appeal the judge’s evidentiary ruling, the proper course of action is for the accused to maintain his plea of not guilty. As stated by a unanimous British Columbia Court of Appeal in R. v. Duong, 2006 BCCA 325 at paragraph 8:
The respondent submits that appealing a conviction in the face of a guilty plea is inappropriate... The respondent recognizes that there are occasions when an accused, after unsuccessfully challenging the admissibility of evidence, may not wish to contest other evidence to be put forward by the Crown but nonetheless may wish to preserve his right to appeal the ruling. In that case, the respondent submits, the proper procedure is not to enter a guilty plea but to admit the underlying facts and invite the judge to convict. I agree with those submissions.
Justice Tidman adopted this reasoning in the case of R. v. Spencer,  N.S.J. No. 563 (S.C.). Following an unsuccessful Charter motion the accused entered a plea of guilty after receiving legal advice that he would still be able to appeal the trial judge’s ruling on the voir dire. Justice Tidman determined that the guilty plea was invalid as it was not properly informed and allowed the accused’s appeal against conviction to proceed.
If the accused does not wish to appeal, there may be an advantage to entering a guilty plea, even at a late stage. A guilty plea is a mitigating factor that reflects an acceptance of responsibility and may lead to a more lenient punishment.
By choosing to enter a guilty plea, however, an accused must appreciate that this will bring an end to any efforts to challenge the substance of the allegation. The only issue from that point forward will be the appropriate punishment, and the only viable appeal issue will be an appeal against sentence.
The bottom line is that an accused must always make an informed decision when tendering a plea of guilty, which includes the loss of a right of appeal of the trial judge’s evidentiary ruling on a Charter motion when the change of plea occurs mid-trial.