Sorry John, but I checked everywhere I could think of and couldn't find the tune to the song on the net. Send me your e-mail address to firstname.lastname@example.org and I will write out the melody and e-mail it to you.
As for the Mira, it is the longest river in Cape Breton. It is situated about 20 miles south of Sydney. I spent many a time getting kicked out of campgrounds along the river, in my younger days. (Usually for singing too loud, or perhaps off key in the wee hours of the morning.) Like Tim has stated, Marion Bridge is a community that grew up around one of the bridges that cross the river. If you ever get to Cape Breton, try to spend at least one day and night on the Mira. It really is a piece of the universe more fit for princes and kings.