I should probably declare my hand in that I think in most cases the
variant stuff is a non-problem (blocking is adequate apart from
where the user is likely to mistype themselves)
According to some people I'm inclined to believe (I can't say this
from personal experience), in non-alphabetic scripts there is indeed a
serious problem with respect to variants. It's not actually like the
case of (say) colour vs. color, because users tend to have access to
one version or another of the "same" character, but that character is
actually encoded under Unicode as a different character. This is, I
am led to believe, a very common problem in areas where, for instance,
Simplified and Traditional Chinese characters are both in regular use.
The upshot is that every competent user of the language will recognize
two different arrangements of symbols as "the same word", each user
will be able to type one or the other of the arrangements (but not
both) at their keyboard, and yet the two different arrangements do not
constitute equvalent labels. So, it's as though by configuring your
system with locale en-CA, you were _unable_ to type "color.com" into a
resolution context. There is a genuine user problem here (though
whether one should actually solve it is still an open question).