Interesting. I was just curious.
On first inspection much of what you have written is bang on.
When the ship was designed (Pre 1985) The sparrow was one of a few choices of PDMS. The MK 41 VLS at the time was earmarked for Standard II, which the Halifax class is not designed to use, being primarily, as you have rightly indicated, an ASW vessel. The other choices of the day were Tomahawks, which you, me and everyone else can forget about Canada ever having, and VLS ASROC, not in the budget.
Now that the Evolved Sea Sparrow has come into being, and with greater oprions for the MK 41, hind sight is always 20/20. 32 VLS in total (16 per side that is) still seems like plenty of PDMS missiles.
As for the Bofors Mk II 57mm, it was reasoned that at the time it would have a greater duo role of surface action against small attack boats and as a secondary PDGS.
Evolving as these discussions naturally do, what role do you see for a 5 in gun on a frigate or destroyer?