I had a similar situation (I am Canadian and was on TN). I successfully applied for a status change via marriage on account of my wife being a US citizen. My attorney said that to get around the temporary intent of the TN status, I had to wait at least 2 months after entering the country before applying for the change of status, in addition to her legal footwork. This meant being able to stay in the country for at least 8 consecutive months (2 months wait, up to 6 months for travel authorization documents), which may be complicated for some. It is possible though.