I figured this out a few weeks ago but I haven't thought to post it until now. The Black Mesa group photo in Kleiner's lab suggests that the HD models from Half-Life: Blue Shift are Canon, notice the different coloured trousers and the id card. The expansion packs may not be canon, but Blue Shift's HD designs might be.
(Edited)
it's like a mixture of both, the clothes from the hd pack and the heads from the originals
No… no… nO NO NO
its so fucking over