Hold in this case means to compare. Comparing apples to apples means the you compare two things that make sense to compare, that are similar enough so that the comparison makes sense. For instance, you would compare one rap artist to another rap artist. This would be 'apples to apples' If you compared a rap artist to a young teen pop singer, it wouldn't make sense, because the styles are completely different and there are very few people that like both. Such a case is called comparing apples to oranges.

to "hold up" apples to apples means to compare them to something else.