For a Crown Attorney, the cross-examination of an accused is a time for asking questions, not making final arguments.
Crown counsel must reserve commentary on the accused’s testimony until closing submissions.
R. v. R. (A.J.),  O.J. No, 2309 at para. 25:
From the outset of the cross-examination, Crown counsel … repeatedly inserted editorial commentary into her questions…. Crown counsel referred to one answer given by the appellant as "incredible". She repeatedly asked the appellant if he "wanted the jury to believe that one too". When questioned as to how he met T., the appellant said he was told by a friend that a relative would be coming to see him, whereupon Crown counsel remarked "so I guess you were expecting some long lost cousin in the old country". After the appellant had described his reaction to being told by T. that she was his daughter, Crown counsel sarcastically said "gee, I guess everybody would react the way you did..."
Statements of counsel's personal opinion have no place in a cross-examination. Nor is cross-examination of the appellant the time or place for argument (para. 29)
R. v. A.G.,  O.J. No. 1217 (C.A.)
…it was inappropriate for the trial Crown to opine with respect to the appellant's testimony that no one would believe "such an outrageous story as you've told… (para. 33)
R. v. Bouhsass,  O.J. No. 4177 (C.A.)
Crown counsel repeatedly referred to the appellant as a bare-faced liar and he regularly injected his personal views and editorial comments into the questions he was asking… (para. 12)