Considering the average Canadian Gun Owner from 30+ years ago probably has the following in their collection:
.22 Cooey
12 Gauge break action Shotgun
.303 Sporter from Grandpa
.410 Gauge to teach the kids
+1 nice hunting rifle with scope
And most of those owners are the ones who never registered with the original registry, many never converted from the FAC to the PAL, they probably have felt no need to do anything since this is all they have/need and they just go hunting once a year, or shoot in the hunting camp.
One of their buddies has a PAL so he buys the ammo for them.
The guns the have are reliable so they don't need to get them fixed.
I'm sure we all know a couple of them.
A 'new' firearms owner in Canada from the past 10 years or so will typically have the following in their collection:
Ruger 10/22
12 Gauge Pump Shotgun
SKS
Cooey they got from some relative for cheap
AR-180/equivalent (non-Restricted Semi-Auto .223)
Bolt Action Ruger American in .223 or 7.62x39
I know of very few gun owners that have only a single gun. They're like Pringles - once you pop, you just can't stop.
Take 2 million, multiply by 5, and you've got 10 million guns.
We all know there's more than that.
As for the 'unknown' number of formerly non-restricted now prohibited rifles of 1500+ makes/models, there is a reasonable estimate of their being almost 2 million of them.