Benjamin Robertson Mitchell

Looking for a US connection to my gr-great garanfather Benjamin Robertson Mitchell born 1880. He is said to have been in Denver before emmigrating to Calgary Alberta. It is also rumoured he and a brother were orphaned and raised by another family. He married Ivy May Milyard and they raied their family on and around southern Alberta. Prior to him conming to Calgary, I have no information. anything would help.
thanks in advance!
Regards, John Massam