A controller is a REALLY good idea on anything over 2000pds, the only good way to stop a trailer that starts swaying is a burst of trailer brake pressure. The X3 is supposed to have some dynamic stability features for settling down trailers but I still wouldn't skip a good controller.
Each state/province has different rules on the max unbraked trailer weight. My understanding is that the wiring is already there it just needs to be connected from under the dash to a brake controller.
https://www.youtube.com/watch?v=cfEt4Ja111w
Plus tow a car on a low trailer, not the one in the video that puts the CG 3ft in the air.