The parallel was established in the 1760s as a border between the provinces of Quebec and New York (including the future state of Vermont). It was measured and marked by John Collins and Thomas Valentine from 1771 to 1773.  In the decades that followed, they each maneuvered to establish sovereignty over the region. In 1825 the governor of the Hudson`s Bay Company proposed a more southern border that would have given the United Kingdom much of Montana and Idaho, almost all of present-day Washington and the entire Columbia River. The Americans rejected that idea. Meanwhile, the United States began to encourage settlers to settle in the Oregon Country, which then encompassed the entire northwest. Such hostile attitudes, both in the minds of the British and the Americans, began to increase tensions between these two nations. The province of Ontario borders the states of Minnesota, Michigan, Ohio, Pennsylvania and New York. The largest international provincial border, most of the border is a water border. It begins at the most northwest point of the northwest corner of Minnesota (49-23`N 95-09`W / 49.383 N 95.150 W / 49.383; -95.150). From there, you will pass east through the Angle Inlet in the Lake of the Woods and turn south at 41-19`N 94`N 48` W / 41.317 N 94.800-W / 41.317. – 94,800, where he went into the Rainy River.  The border follows the river to Rainy Lake, then through several small lakes, including Namakan Lake, Lake cross and Sea Gull Lake, until it reaches the Pigeon River that leads to Lake Superior.
The border passes through Lake Superior and Whitefish Bay, into the St. Mary River, and then into the North Canal. AT 45 degrees 59`N 83- 26`W / 45.983 N 83.433 W / 45.983; -83.433 the border turns south towards the False Detour Canal, from where it reaches Lake Hurone. Across the lake, the border leads south to the St. Clair River, which leads to Lake St. Clair. The border passes through Lake St. Clair and reaches the Detroit River that leads to the Erie Sea. From Lake Erie, the border leads to the Niagara River, which leads it into Lake Ontario. From there, the border goes northwest to 43-27`N 79-12`W / 43,450 N 79,200 W / 43.450; -79.200, where it makes a sharp turn to the northeast. The limit then reaches the St.
Lawrence River, through it to the end, at 45-00`N 74`40` W / 45,000 N 74,667 W / 45,000; -74.667 the border separates from the river and continues towards Quebec City.  This treaty provided that the commissioners had to decide on the sovereignty of the various islands in Passamoquoddy Bay, that they had to determine “the northwest corner of Nova Scotia” and the northwest head of the Connecticut River, and that a map representing the border would be established. The “The North Line” section of the border, which stretched from the source of the St. Croix River to “the northwest corner of Nova Scotia,” was measured and marked in accordance with Article V of this treaty. Sections VI and VII provide that commissioners must set the boundary between the 45th parallel and the most north-westerly point of the forest lake. Under this contract, an agreement was reached on part of the border, but parts of the route across the St. Mary River and at the top of Lake Superior were not agreed upon. Signed in December 1814, the Treaty of Gant ended the War of 1812 and returned the borders of British North America and the United States to the pre-war state.