The version I learnt in high school drama class was:

Rose, rose, rose, red
Will I ever see thee wed?
Aye, marry, that thou wilt
When I am dead

It was explained to us that the word "marry" in the third line is the archaic interjection meaning "indeed!" and, confusingly, has nothing to do with "marry" in the sense of marriage (though the rest of the song is about that).

We were told the song was about a woman refusing to get married, and she's saying the only time she'll be "married" is when she's dead, which she sees as being married to death.

I learn this version in Queensland, Australia.

By the way, I'm finding all these subtle variations of the song fascinating. It's amazing how much the meaning can change with just a few changed words, or by substituting homophones.