While watching the Star Wars Holiday Special a segment near the middle includes a cartoon where C3PO talks about a virus that only effects humans (referring to Luke who had previously passed out). Is the Holiday Special considered canon?
The movies themselves featured Luke and other characters being referred to as "human" on occasion--in The Empire Strikes Back, when C-3PO is commenting on Luke's chance of surviving a night on Hoth, he says "He's quite clever you know...for a human being." And in a later scene when they're hiding inside an asteroid, Han gets angry at C-3PO for stating the obvious and C-3PO says "Oh! Sometimes I just don't understand human behavior." Finally, he repeatedly states his job description as "human-cyborg relations". This doesn't really settle the question of whether Luke would show up as human on an Earthly DNA test, though--"human" in the language Galactic Basic Standard might mean something a little different than what it means in English, even though the two languages coincidentally happen to sound identical. Note that in the current canon, humans are said to have originated on Coruscant (established in the canon game Star Wars: Uprising), which would at least imply a different evolutionary origin.
As for the other question about whether the Holiday Special is canon, 2014 the definition of "canon" was changed to prepare for the new movies, and the Holiday Special has no current canon status at all. Prior to that, as described here there was a descending series of "layers" of canon, where each layer had to respect the canon of stories on the same level or higher, but could ignore or rewrite things from lower layers; as mentioned here, the Holiday Special was considered to be S-canon, which is the lowest of the layers that were considered to have any degree of canonicity (as opposed to completely 'non-canon' stories).