That was "Ame Caline (Soul Coaxing)" by Raymond Lefevre & His Orchestra. I don't think that it made the Labor Day 500 the first several times that the votes were conducted, but then a certain Canadian (whom I'll refer to as "L") started posting about how he had looked for this song for a long time despite not having even heard it for many years, because he liked it so much. Then it started appearing on the LD500 and Ron commented on it getting a lot of votes from Canadians, which may have at least partly been because it was a bigger hit in Canada (it only reached #37 on Billboard, but got to #19 on CHUM). I have it on good authority that Ron's comments came as a surprise to L, but he didn't mind it at all ... he even started alleging that there was a Canadian conspiracy involved, and that he was at the centre of it. Ame Caline did get quite high on the LD500, but then started dropping significantly on subsequent surveys ... I don't know how unpopular it became, but maybe L was a bit too successful with his Canadian conspiracy allegations. It's probably just as well that we're no longer doing the LD500 here, given that we now have a Canadian running this forum. 

I was curious if it would be possible to access the old Labor Day 500 lists via the Wayback Machine. I found that it is, at http://www.oldiesmusic.com:80/500.htm">https://web.archive.org/web/20180913020905/http://www.oldiesmusic.com:80/500.htm. And more specifically, you can see how each song did year by year at 
http://www.oldiesmusic.com/2015cumulativeld500byartist.pdf">https://web.archive.org/web/20170420221059/http://www.oldiesmusic.com/2015cumulativeld500byartist.pdf.