Basically, Margaret Douglas was seriously proposed to four men prior to the scandal with Thomas Howard. Although many others were put forward, these men came the closest to marrying the sister of the King of Scots and the niece to the King of England. These men were:
James Stewart, 1st Earl of Moray: The first Earl of Moray (
not this guy) was suggested as a match for Margaret Douglas around 1519/1520, when the girl in question was 5 years old. This match was dropped due to fears that a match with a legitimate "Princess" might give the Earl ambitions to the throne, and because Margaret Tudor felt it was beneath her daughter.
Patrick Hepburn, 3rd Earl of Bothwell: This Earl of Bothwell (
father of this terrible human) was proposed as a husband for Margaret Douglas in 1528, as a suitable Scottish match, preventing the English from taking her. Her father was quite interested in the match, but her mother was not. While it is likely she was still in her mother's care at the time, Margaret is said to have sided with her father, partially because the man he wanted her to marry was known as "Fair Bothwell" due to being blond and attractive.
Sir James Stewart: Brother of her
mother's husband in 1528, Margaret Tudor apparently wanted him to marry her daughter, which is weird, but as she was most likely in her care in 1528, quite possible.
Alessandro de' Medici, Duke of Florence: The only real match I know of that was close to happening at Henry VIII of England's court prior to the Howard issue, this Medici match was put forth because Henry VIII wasn't going to let Mary marry into Italy, so Margaret was put forward as an option.
Personally, I think the Hepburn match is the most likely, but the Medici match would be the most interesting. Thoughts?