The point at which America can impose terms on Britain one-on-one is either in the 1890s before the Spanish-American war or after 1906 with the launching of the Great White Fleet. At these points America has a large enough standing army to invade Canada and a large enough navy to force the UK to retreat from their periphery to fight the naval war. The US could build up shipbuilding capacity and seaforts during the war to an extent where the British would lose the war of attrition.
The United States became the largest economy in terms of GDP ppp in the 1870s and surpassed Britain in most industrial aspects by the late 1880s/early 1890s. I'd therefore say sometime during this period.
Okay a couple of related points so I thought I would address them in the one post.
I am deeply opposed to the 1890s as the point at which the tipping point between British superiority in the border regions/ coastal areas of the USA switches to US superiority. For a start the US Army was actually in something of a nadir prior to 1898 and so by and large no the US does not have the standing army to invade Canada...as to the Navy...it might interest people to know but Alfred Thayer Mahan's plan for a possible war with Britain in the 1890s basically revolved around the battleships of the US Navy forting up in New York to endure siege. The cruisers of the USN were to conduct commerce warfare against the British Empire. This is not a Navy remotely close to be able to impose control of its home waters.
1906 does see a change in that the US Navy at around this point does have the kind of battle fleet that can interdict landing operations on the US East Coast...it takes a while before the US could muster a fleet that could divide into two to provided the same level of cover for both oceanic coasts. It is a further stretch to suggest it might be able to sever the sea lanes to Canada, that point was not likely reached until the 1920s with the Washington Treaty and even then the RN still remained confident that while it could not support a full up deployment of the British Army to Canada it could cover sufficient convoys to maintain the defence of Nova Scotia and especially Halifax.
Now as to the notion the 1870s marks the tipping point...a lot of people look to total war without actually asking what is involved in providing for a total war. Civilians it turns out do not come pre-equipped with the standard service rifle, pack and webbing/harness, uniform including stout boots and at least six months basic training. In the Spanish-American War the US was able to over provide two things uniform kit and warm bodies...the break down occurred in training personnel and the logistics support between railheads/beachheads and the actual units in the field. In addition but the US forces were only sparingly equipped with field artillery which might have been an issue against the British who would be rather more fully equipped.
In each of America's war be it the Civil War or the Spanish-American War or World War 1 and even World War 2 we see foreign inputs go in to equipping the US War machine. The idea that the US will simply shrug off a British blockade and happily total war their way to power is questionable.
In the 1870s for example the US have a legacy fleet from the Civil War but technology has moved on considerably since then. The monitors designed for bashing Rebel river and coastal forts are not entirely suitable for facing contemporary sea going ironclads and even less so when those same vessels have been up-gunned with modern ordnance. The Civil War artillery kept in stock amounts to some 100 Napoleons and 100 Ordnance Rifles plus a number of howitzers. The supply of small arms is better the 1873 Springfield conversion is up to date for the period and plentiful. The US Army starts the decade nearly 40,000 strong but falls to 26,000 by the end of the it.
Of course things will be different with preparation but the US needs to prepare for years in the 1870s as pretty much it needs to do at any point certainly until the 1920s and even then it would be advisable. This preparation is also likely to provoke an Anglo-Canadian response and even something as simple as proper fortifications on the Canadian border makes a US assault that much more problematic.