Well, the first obvious opportunity for judicial discretion is at the time the crown applies under section 752, when the crown may have to make argument to the court that in fact the predicate offence is a serious personal injury offence. If the judge finds it does not meet the section 752 criteria, at that point he can rule under his discretion that it does not meet the threshold and it can't go any further.
The next opportunity for discretion, if it passes that initial threshold, is that the crown must apply under section 752.1 for a psychiatric assessment. The judge has discretion at that time to stop the application there if the judge is of the view that it's not likely to result in a dangerous offender designation.
Once the assessment is returned and filed with the court, the crown then has to seek and obtain and table in writing the Attorney General's consent. If that is done, along with notice to the defendant, then it goes into the hearing phase. At that point the final exercise of discretion of the court is first of all whether the offender meets the dangerous offender criteria; then, per the decision in R. v. Johnson, even if the offender does meet dangerous offender criteria, the court of course may refuse the indeterminate sentence if in fact a lesser punishment is available to manage the risk posed to the general public.
Under the new provision, all those discretions are retained. Even in the circumstances of the presumption kicked in by a third sufficiently serious predicate offence, the judge still has the discretion, if the offender is able to rebut the presumption, to refuse the designation.
In either case, if the designation is made, then again the qualification of the Johnson principle is very clear: the judge retains final discretion to not impose the indeterminate sentence if the risk to society can be successfully managed under a lesser sentence.