This time of year I tend to see people trying to make a son-sun connection when talking about the origins of Christmas. This seems pretty ahistorical to me, since sun=son is an English similarity and doesn't work at all in, say, Latin (sol = filius?). However, as far as I can tell the two words are at least vaguely similar in Greek.
Which brings me to this two-part question: would the words for son and sun have sounded similar to Greeks 2000 years ago? And are there any works written in ancient/classical Greek that directly draw a connection between the words for son and sun (in any context)
To answer your first question, about their similarities: they would have been written huios 'son' and helios 'sun'. I'm not a Hellenist, but I'm pretty certain in the relevant time period the first vowels in each word (the u and e) would both have been distinct, with /y/ (like in French tu) for 'son' and /i/ for 'sun', the /l/ would still be there in 'sun' (as it is today), 'son' would have 2 syllables and 'sun' three, and 'son' would have stress on the final syllable and 'sun' on the first.