The correct option is the first one: The Oregon Country was divided between Britain and the United States ath the 49th Parallel.
After the outbreak of the Meican-American War, the US decided to negotiate with the British the division of the Oregon Country instead of trying to annexionate the whole territory. With the sign of the Treaty, the border between the USA and British North America was drawn by the 49th Parallel except for Vancouver Island, which remained under British control.