I too have a vague family story about two brothers, James and JOnathan Dow who came over from ??? and split up with one going to Nova Scotia and the other going to the New England states. There was certainly a connection between the Dows in NS and those in NH. The story about the two brothers continues to crop up in various places, so I do expect that it has some truth to it.
There is a Samuel Dow family that was living in Cumberland County NS atthe same time as my William Dow family. I have not been able to place Samuel at all, so he is either the son of one of William's brothers or the son of the other Dow brother. Martha's family name is misspelled as Haladay and Halada on the census(es) for 1871/81/91 in NS. Both lines tended to name their children similarly and marry into local families like the McCullys, Ayers, Cannings, Bowdens etc so it has been a bit difficult to separate them. I remember my uncle George Tippett talking about an Aubrey Dow, but I don't remember what connection he had to our line.