I am using G, C and D

[G] Step we gaily on we go
[C] Heel to heel and [G] toe to toe
[G] Arm in arm and row for row
[C] All for Mari's [D]wedding

and same for verses

but I have also seen (JC's music site)
http://ecf-guest.mit.edu/~jc/music/abc/findtune.html

[G] Step we gaily on we go
[C] Heel to heel and [D] toe to toe
[G] Arm in arm and row for row
[C] All for Mari's [D]wedding

If you do a search on Google or elsewhere you can pick up another variation that uses A, D and E7 (not bad ). There is even a further variation that I found but when I tried it, it sounded poor, it must have been wrong.

The chords are also in Van Morrison Irish Heartbeat album, fulls sets of chords and lyrics from this album can be found in various places on the WWW.

e.g. www.freewebcity.com/vantab/tabs/irish_heartbeat_album.html