The first US move into Canada in 1812 ended on 16 August, when Brigadier General William Hull surrendered Detroit to Major General Isaac Brock. The Americans subsequently defeated an attempt by Britain’s Native American allies to capture Fort Wayne.
Jeremy Black notes that conquering Canada was the USA’s principal strategic aim, but that it is uncertain whether President James Madison wanted to keep it or just to use it as a bargaining chip in negotiations over the USA’s grievances with Britain’s conduct of its naval blockade of France and its allies; impressment of US sailors into the Royal Navy and British interference with US seaborne trade.
Canada had a population of 4-500,000, compared with 7.25 million in the USA. The frontier was long and the British garrison was small; less than 10,000 troops and only two warships on Lake Erie and three on Lake Ontario. The war with France was far more important to Britain than the defence of Canada. 
The state of communications and relations between their commanders made it hard for the Americans to co-ordinate operations. Logistical and political problems prevented them to concentrating their state militias into a single force.
The Americans suffered from the difficulties encountered by any army that grows rapidly. There was also a lack of clarity in the relationship between officers of the regular army and those of the state militias. They had supply problems and some militia units refused to fight outside the USA.
Britain had conquered Canada in 1759-60 by an attack on Montreal through the Lake Champlain corridor. However, this required major logistical planning and resources and came after several years of failure.
Despite the long frontier, the potential invasion routes were limited and a well positioned defending force could stop a larger attacker. Water communications were significant, especially the Great Lakes, but were more useful for east-west than north-south movement, except for the Hudson/Mohawk route.
Black criticises Lieutenant General Sir George Prevost, governor-in-chief of British North America and C-in-C of all British forces in North America, for moving Brock and troops to defend the Niagara front rather than exploiting the victory at Detroit.
In October the Americans crossed the Niagara River. William Eustis, the US Secretary of War, said that:
[T]he march to Detroit by the way of Cleveland is near 300 miles – that to Niagra not much more than 200, the former through a wilderness, the latter principally thrtough a settled country…provision to and at Niagara more plentiful and less expensive by 50 per cent.
There were also fewer Native Americans, who were generally pro-British, in the west.
The senior US regular officer on the Niagara front, Brigadier General Alexander Smyth, refused to cooperate with Major General Stephen Van Rensselaer, a militia officer who was put in command. He had 1,650 regulars and 4,300 militia facing 1,600 regulars and militia and 600 Iroquois.
The Americans crossed the river on October 13, landing at Queenston despite strong currents and British fire. The British attacked and Brock was killed. The Americans held their positions, but were hampered by the reluctance of some militia units to invade Canada and Smyth’s refusal to obey Rensselaer’s orders. Shrapnel fire from British cannon silenced the US guns and sank US boats.
The Iroquois won time for Major General Roger Sheaffe, Brock’s replacement to bring up reinforcements. The Americans had either retreated back over the river or surrendered by the evening. The British took 925 prisoners and claimed to have killed or wounded 500 Americans. According to Andrew Lambert, this victory was very important in creating a Canadian national identity.
Smyth replaced Van Rensselaer after the latter resigned on 16 October. He planned to capture Fort Erie, a vital position according to Black. On 28 November the Americans raided Frenchman’s Creek in preparation for a larger crossing of the Niagara. It was partially successful, but Smyth cancelled the major assault on 1 December because he did not think that he had enough troops to succeed.
Brigadier General Peter Porter accused Smyth of cowardice. The pair fought a duel on 12 December, but neither was injured.
In the Lake Champlain area a US attack on Montreal from New England was abandoned because of logistical and command problems. Major General Henry Dearborn, the US commander, offered his resignation, but Madison rejected it.
Despite these failures Madison was narrowly re-elected as President in November 1812. However, his opponent, DeWitt Clinton, won all the coastal states from New Hampshire to Maryland. Clinton did not oppose the war, but those who did backed him because he was not Madison.
Madison accepted Eustis’s resignation. Secretary of State James Monroe became acting Secretary of War at the end of 1812, with John Armstrong taking up the post on 5 February.
US resources had proved to be inadequate to carry out their planned land operations against Canada. Russell Weigley contends that the US Army failed to recognise the need to concentrate on the enemy’s most important and vulnerable point; the bottleneck on the St Lawrence River at Montreal, which controlled access to the interior of Canada. However, American morale remained high because of their unexpected success at sea.
 J. Black, The War of 1812 in the Age of Napoleon (Norman: University of Oklahoma Press, 2009), p. 46.
 Quoted in Ibid., p. 67.
 A. D. Lambert, The Challenge: Britain against America in the Naval War of 1812 (London: Faber, 2012). Kindle location 1272 of 12307
 Black, War of 1812, p. 69.
 R. F. Weigley, The American Way of War: A History of United States Military Strategy and Policy (New York: Macmillan, 1973), p. 48.