Howdy:
My apologies for the delay in seeing and responding to this thread .... haven't been here for a while.
The plate
may be a variation of a Canada Militia "General Service" shako/helmet plate, supposedly dating from 1870 and thereafter, such as this one depicted in Daniel Mazeas' "Canadian Militia Badges Pre-1914" (which you will note has a wreath of leaves like those on a British helmet plate of the era) -
.... or this original (which has a wreath of maple leaves) -
To be honest, however, the Canada Militia center of your plate is not the correct size for this pattern of helmet plate, and looks more like the center from the somewhat smaller (i.e. about 1 1/4" diameter circle) pre-Confederation Canada Militia shako plate, which looked like this -
In fact, from the appearance of both components, I am unfortunately of the view that your plate might well be a relatively modern attempt to simulate the appearance of a Canada Militia General Service helmet plate by using a reproduction British helmet plate body (designed to be used with a separate unit-specific center which would cover the raised lip around the opening) together with a reproduction Canada Militia shako plate center. (These items have been reproduced for use by modern reenactment units and the like.)