[wideminded]

I understand also that there is a thought that Arthur used the birth certificate of his prother to prove that he wasn’t bon in Canada.

I haven't heard that but I do know that historians now say there was no doubt Arthur was born in the US. Arthur was accused of being born in Canada and Ireland, but for some reason the issue his father's citizenship was not brought up as a disqualifying factor at the time. Of course Arthur was elected as Vice President and became president upon the assassination of Garfield.

[MHGinTN]

“... but for some reason the issue his father’s citizenship was not brought up as a disqualifying factor at the time.” Because Arthur lied, stating a false date for his father’s naturalization. In fact, his father was naturalize years later than what Arthur claimed, and Arthur had all his presidential papers burned to cover his lies.