On occasion, appellate courts have reduced a sentence which was fit when imposed because of the significant progress the offender made while awaiting the hearing of the appeal. 

The offender is required to establish that he/she has taken something akin to “very unusual significant strides” or “extraordinary rehabilitative efforts” since the original sentence was imposed, and — typically — that the sentencing objectives have been met by the offender’s extraordinary efforts.
The exercise of this appellate discretion is exceptional. 

As the Court of Appeal for Ontario noted in R. v. L.S., 2017 ONCA 685, at para. 117, in most cases, positive steps taken by the appellant between sentencing and the hearing of an appeal are best dealt with by the correctional authorities.  The appeal court cannot act as a de facto parole board, but must trust the parole authorities to exercise their powers to facilitate the appellant’s reintegration into the community at the earliest appropriate time.

It should be noted, however, that in R. v. L. S., the principal goal underlying the appellant’s sentence (denunciation) remained as vital as it was when the sentence was imposed.

Contra, see the leading case of R. v. Ghadban, 2015 ONCA 760 (CanLII).

Where denunciation comprises a primary sentencing objective

When an offence calls for a denunciatory sentence, the length of the sentence imposed is most often the means used by the court to send the denunciatory message.  An appellant’s positive lifestyle while on bail pending appeal does not justify departure from that norm.

R. v. L.S., at para. 111.

However, see R. v. Ramta, 2017 ONCA 580, where the same Court found that the public interest would be better served by allowing the appellant to continue his efforts to become a productive member of the community than by emphasizing denunciation and general deterrence. Sentence varied to time served.