According to Alan Mills, "Mary Ann" is a Canadian derivative of the Enclish love song known as "The True Lover's Farewell","The Turtle Dove" and porbably other titles. He further claims that the English song inspired Robert Burns to write "My Love Is Like A Red Red Rose".
John is right in that the Easy Riders recorded the song long ago, it was even one of their album titles. I first learned it from a version by the canadian folk group, The Travellers. There is also a version sung by Charles Jordon on record IV of the Canadian Folk Songs Centennial Collection. But if you are looking for a current version on CD, an excellent one is found on "Never Grow Old" that was put out a few years ago by Priscilla Herdman & Cindy Mangson. You should be able to get it from one of the online "record" stores. Tom Paxton joins the two women on the song. I am sure you would like it.