Thanks David, First I thought "married 1868" is too late for my couple, but when I look at the original document it is 1848, which is about right, as their eldest child Marjory was born in Dec 1847. The Find-a-Grave link is correct and one I am very familiar with - note that in nearly all records John Alexander Fraser is either "Alexander Fraser" or "Alex Fraser".
Now the issues: I don't have a son James B born 2 Dec 1867 listed for the family. But that is ok. So far...
Next, I have the whole family, Alexander and Catherine and including all the children I known of (Marjory, Lachlan, Archibald Norman, Hume, Christina Margaret, and John Alexander - note no James) living at Stanley, Huron South, Canada West (Ontario), in the 1861 Census
They were living in Ontario by 1860 (their youngest son John Alexander was born in Ontario) and so are not the same couple as the one you found in Middle River. They were still at Stanley for the 1871 Census, but moved to Portage La Prairie later in the 1870s.
Thanks much though - I was pretty excited to see this lead! I will keep looking....