What makes you think there is a connection? I have no Shaws in this McClellan family's history. If you have more info, maybe I can help.
The last name is McClellan no D and not MacClellan with or without a D.
John Unger McClellan is the son of William McClellan 1804- 1881 and Emmeline Unger, Grandson of John McClellan 1774- 1868 and Jane Thompson and grt grandson of William McClellan 1747-before 1833, he emigrated from Ireland to upper New York state in 1768.