I am sorry, I don't know much about the Dean. The only Dean I know was an illegitimate nephew of Michael Whitmore's son Michael and his wife. His father was Irish, but his mother came to Canada in 1847 and the child was born in Canada probably in the house of her sister. I don't see any connection.
Michael Whitmore and Mary Fisher were married October 18 1814 in York. Mary was a daughter of Jacob Fisher Jr of PA. The Fisher have been well researched. Their children were all baptized in Zion Lutheran church in Vaughan twp, York County. Transcripts done by the Ontario Genealogical Society.
Michael Whitmore (1758-circa 1859) is a bit more difficult. According to his Upper Canada Land Petition of 1825 he was a native of Pennsylvania, and he came to Upper Canada around 1800.
He served on the Canadian side in the War of 1812. He asked for compensation after the war.
I think he came with Michael Dye, who was a witness at his wedding. Around 1825, Michael Dye, of PA, died in King Twp, York County where he was a tavern keeper and he left all of his estate to his friend Michael Whitmore. He also asked Michael to take care of his widow Mary Dye. There was no inventory with the will, but Michael Dye owned quite a bit of property.
At some point, Michael Whitmore owned a sawmill on Yonge street close to Gallow Hill. He also owned a tavern, as well as a Pottery on Yonge street who burned down in 1830.
I have not been able to connect Michael Whitmore to a specific Whitmore family in PA (there are many), but at some point Michael and Mary went back to US, possibly because of the 1837 Rebellion. After 1837, his name no longer appears on list of tavern keeper in Home District. He was charged with perjury and left Upper Canada. Quite likely the case is related to the Rebellion and maybe some of the other Canadian friends might also have left Canada for political reasons.
In 1872, the eldest grandson of Michael and Mary, called Michael Dye Whitmore, is living in Allegheny, PA. I think it might have to do with inheritance of some kind.
Michael and Mary had at least 8 children: Michael Dye Whitmore( wife Catherine McClelland), Susan (David Dray & Lorenzo Huntley), Mary Ann (Loren Day) Catherine (Hugh McQueen who was deceased in 1872), Samuel(Sarah Kaiser), Henry (Margaret Cotterell), John (Mary Kingston, born in Ireland), Jacob (Marianne Godfrey both of them were deceased by 1872 and had only one child William alive).
Maybe some of these names will ring a bell. If you know where Michael Whitmore is buried, I would be most interested. His wife lived alone in a house close to Yonge Street in York twp, York county, in what is now part of Toronto. She died there, but her husband is not with her, and quite likely she left him. Her father left land and money to her children but not to her nor her husband.
The Whitmore are generally described as PA dutch, but even though they were Lutheran in Canada, they might not have been German or Dutch at all originally, but intermarried with PA Dutch family like the Fisher.
Good luck finding your connection. It might be useful to know which Whitmore woman was a sponsor of the child, and whether she was the wife of one of the sons.
Most of the grandchildren remained in Canada and York, except for the eldest grandson Michael Dye Whitmore Jr who moved to Allegheny, and can be found there with his wife and family.