There are many Web pages about the Dow Brewery in Montreal, this one gives the dates of death of the two brothers, so if you obtain copies of any death records and also search for obituarries in the local papers, these may give you clues as to their origins-
Bearing in mind that there can be confusion between where a person was born/baptised and where that person "came from", there is a couple, William Dow and Anne Mason married 1800 in Aberdeenshire with a first child born that year, then apparently moving to Perthshire and Muthill eventually, with a later son Andrew born 1809.
Use the Family Group facilities of familysearch to find them-
Generally if you are satisfied that the records found on familysearch are likely to be relevant, you should order photo-copies from Scotland's People as frequently the original document has comments, notes etc that do not appear in the on-line index.
But cross-check everything carefully!!
Gang waurily, dinnae spend y'r siller 'til y'r shair!