Condolences, Paul. There are three tunes I'd suggest. None are "waltzes" per se, but they may be suitable for your purposes:

Duncan Bàn MacIntyre's Màiri Bhàn Òg
This song was written by him when he married his wife. They apparently lived a long and happy time. This was back in the late 17th century or 18th. It's timeless and been both sung, and just as an instrumental. On a number of recordings from Cape Breton, most recently Jackie Dunn's Dunn to a T
 
Maurice Leemon's If Ever You Were Mine
This has been only around for about 20 years, but is a very popular tune to dance to in the Nova Scotia area, among the Cape Bretoners. It's an Irish tune, and a CFA, Silver Donald Cameron wrote a wonderful song to it for his wife, Lulu. She recently passed away too. It was sung on Scott MacMillan's Minnie Sessions' Volume 1. The tune by itself is on Natalie MacMaster's Fit as a Fiddle.
 
Niel Gow's Lament For His Second Wife
This is somewhat of a standard here in the Maritimes since almost EVERYONE plays it. My current favourite version is by a young lady, Màiri Rankin of Mabou. She's only 18, but is a phenomenom with this tune.