Just a note - I am not much use on the US side - I would like to help but I have not researched the US families in detail.

Comments that I might make kindly are:
It is HUGE - it appears that there are a mighty lot of Caldwell descendents in the US - some like the "Cub Creek" family seem to have been well documented however there must have been many, many original sources.
For instance I know that a brother of my GGGGrandfather Allan Caldwell emigrated to become a miner at Cape Breton Nova Scotia - he died there not long after emigrating and his widow re-married. At least two of his children "disappeared" into the USA through Boston and other descendents moved deeper into Canada.

Perhaps our US cousins could try and narrow things down to a more limited number of family line sources at time of emigration and then collectively hunt out information on these original settlers. Some have already done this and forgive me if I seem presumptious.

Questions like "Looking for Charles Caldwell married to Jane Smith b Appaloosa County" seems a bit like randomly firing a shotgun in the air and hoping to hit a sparrow. Luckily we are all out here to try and help one another.

A bit of original research at the local library or historical society or from some web-trawling reported on this site (with sources) is an invaluable help and very much appreciated by all.