First, if it's looking like one, it does not mean it is a variant.
RCMP might see it as a variant
if and when they will have one in their hands,
but until then let's not make assumptions.
Specifically, let's not make RCMP's job now.
Secondly, there is at least one Umarex in the country like described in the OP.
It was marked both Walther and Umarex (because Umarex is owned by Walther).
I have seen it. Deal with it.
Pretty much everyone I've inquired to about one...MP5 variant...though it shares no parts at all. Just looks...I say we get a couple people together and order one off of the IRG U.S. site and see what happens...that'll give a definitive answer.
CBSA will not allow into the country any firearm without classification or the firearm being submitted to the RCMP lab.
That is in their regulations.
However, it is not clear where in the law it sez that all the firearms already in the country have to be classified.
That's the catch

If, for example, one makes a gun home, (without intention of selling it, etc.),
where does the law say that it has to be submitted to the classification process?
People normally assume that it should, but I can't find that detail in the law. Come on, show me.
Eg, there are quite a few firearms in Canada since many years (since before December 1, 1998, anyway),
that are not to be found in the FRT tables.
These firearms survived 15 years of registry law,
they probably changed few owners, they got used, but never got classified.
And that is a fact.
Are these guns illegal because they have not been classified/submitted for classification?