I can see how a particular firearm could meet the criteria of both, but in the end there are two separate definitions for "antique firearm" and "prohibited firearm". This part: references this:
http://laws-lois.justice.gc.ca/eng/regulations/SOR-98-464/page-2.html#docCont
The wording of CC 84 opens up a grey area, but I would say that in general, the statute has more weight towards "antique" in this scenario.
What you have quoted is irrelevant. How a firearm comes to be antique, whether meeting condition 1) Pre 1898 manufacture or condition 2) prescribed by regulation, doesn't matter. Antique is antique.
There is no grey area. Yes there are two definitions, antique firearm, and prohibited firearm. Are you choosing to ignore the fact that I have quoted several additional definitions, all of which can be applied to a single firearm? Shotgun and Rifle are not defined in the criminal code, but those words have dictionary meanings and they are given legal statuses that are separate from a handgun, which is defined. As one example, the definition of prohib includes firearms adapted from rifles or shotguns to have a barrel less than 457mm, firearms which typically have been NR without the modification. This is contrasted with the fact that Handguns at a minimum are restricted, and handguns only become prohibited at a length of 105mm. Clearly the law intends that rifle and handgun be treated as separate mutually exclusive categories.
The classification definitions however, do no such thing.
Imagine a shotgun that is sawed off at the barrel and stock with the intent of making it capable of quick and easy one handed firing, such that the modified shotgun is 600mm in length with a 300mm barrel. This firearm would be both prohibited AND restricted, because it is both NOW a handgun, having been altered and intended to be aimed and fired one handed AND it has been adapted from a rifle or shotgun...
Even if you want to contend that antique is a class of its own (it isn't) separate from NR, Res and Prohib, once again, nothing sets up antiques, prescribed or otherwise, as being mutually exclusive from other classifications. Especially not when you read S 117.15 (3) and (4) of the Criminal Code.
(3) Despite the definitions prohibited firearm and restricted firearm in subsection 84(1), a firearm that is prescribed to be a non-restricted firearm is deemed not to be a prohibited firearm or a restricted firearm.
(4) Despite the definition prohibited firearm in subsection 84(1), a firearm that is prescribed to be a restricted firearm is deemed not to be a prohibited firearm.
Note that this mutual exclusivity provisions only affect firearms PRESCRIBED into one class or the other, and not those based on the physical characterists. Nowhere in the code or the antique regulations carry language of this sort.
It sure would be nice if the law did set antiques apart as a class of their own, but alas, the law was written by adult children who have managed to do more damage with their legislative crayons than any normal person will ever do with a firearm.