Can't help with the insignia questions, there are probably more knowledgable people around. I'd expect to see 3 Cdn Med Regt, but I'm not certain. They were administratively grouped into an AGRA, and that formation was controlled by First Canadian Army. They would then be assigned as needed, often to 2 Canadian Corps, but for Veritable, actually under control of 30 British Corps. Best I can explain it, he worked for 3 Cdn Med Regt, who were given tasks by the AGRA, who were given tasks by a Corps, who were given tasks by an Army.
I found links to the War Diaries for 3 Cdn Med Regt here:
Lots of stuff there to dig through if you are inclined.
From these, you may be interested in:
Start of War Diary for Feb 45:
Location Statement for 2 Feb 45 (I assume no move before 8 Feb 45 based on unchanged Map Reference for RHQ):
I have created a simple Google map with locations for RHQ and the four Troops of guns for Op Veritable:
Hope that link works. You'll have to determine which Tps were associated with which Btys.
I used this tool, coordinates are not precise but usually within 100m-200m. You would need a period map to check.
Part I Orders for 24 Dec 42:
Quality is poor, but worth a look to see if you can find the entry for his TOS (under the heading Strength Increase). Looks like they often record which Bty new men were posted to, so may help with research. Publishing this info could sometimes take days or weeks, but this would have been a fairly quiet time, so hopefully he appears in the 25 Dec list, I see no others to the end of Dec.
I'd expect to see a similar entry in Pt I Orders (Strength Decrease) when he left the unit. A quick scan through Feb 45 does not show any Strength Decrease entries, so they may not have been publishing them, or they may appear several weeks later when they caught up administratively.