alternatehistory.com

25 April
The initial crossing by the US troops is made at dawn. 2,500 troops cross the Niagara river in the first wave, taking light fire from Canadian militia pickets (which are engaged by the Union artillery on the east shore in turn, and firing into the sun) and take approximately fifty casualties before getting across and establishing a beachhead. There is a short, sharp action which leads to the Canadian militia companies falling back in rout, having taken heavy casualties and some troops captured.
Much of the US-controlled lakes shipping is now brought into action, ferrying troops across in a continual stream so that by 8am (around an hour and a half after sunrise) the US force has all moved to the western bank, including all their artillery. Notably, there is a new innovation - the ~18,000 troops sent are accompanied by about 2,500 civilian drovers, as the commander of the Union forces has elected to put all his rifles on the firing line. This effectively increases his force compared to a normal army of the same size, though it does make the supply train more vulnerable.
Similarly, the artillery are not armed with any personal weapons and are supported by civilian volunteers, and consideration was given to stripping the cavalry of their long arms as well - though this was not taken up. All this means that the Union force is actually slightly larger than its weapon allotment would normally allow.


The British commander has heard of the Union crossing, and considers an attack to drive them back across the river. Quick contemplation makes him realize this is unlikely - any window of opportunity has likely passed - so he begins moving forces southwards.
He is cautious, and does not strip the defences - not knowing for sure the size of the Union force to his east, he considers it possible another attack in the same or greater strength may be about to happen on the southern end of his line.
The nearest Cavalry regiment is a unit of Canadian militia cavalry (the Royal Montreal cavalry, a name which has caused a few chuckles among bilingual Canadians) and these are sent forwards to keep track of the Union troops. While this is taking place, the Regulars (2 battalions, the 31st and 32nd foot) deploy forwards, with skirmishers ahead of their supports.
In keeping with standard British doctrine, the Regulars have their skirmishers deployed about half a mile in front of the main line - this means in effect that the support column is behind a hedge two large fields ahead of the main line, and that the skirmishers are another fifty yard ahead in pairs.
Most of the Canadian militia are in the main line, with some of the more experienced flank companies joining the Regular skirmish line and one regiment of Canadian militia in the support column. As such, there are about 400 regular infantry and 1,000 militia in the skirmish line and the same again in the support line.

The American formation encounters the Royal Montreal cavalry around a small farmhouse. The Canadian cavalry has been ordered to merely keep track of the Union troops, but the Colonel is not experienced at controlling an entire regiment under combat conditions and is unprepared for some of the Union 12-lbers to engage his horse with grape. This and a volley of (long ranged, inaccurate, but intimidating) rifle fire scatters them, and the Royal Montreals will take around half an hour to reform with ~200 casualties - most of them missing.

At about this point, the American scouts enter the fields covered by Imperial skirmishers. Rifles crack, and at this range (400 yards, very roughly) the Canadians are inaccurate but the British regulars are very accurate indeed. The American cavalry is driven back, and contact reports go back to the main American column.

It is now around 10AM, and the American commander is preparing his attack. The first attempt to set up artillery results in several casualties from sharpshooter fire, so the guns are pulled back behind the hedge line and orders distributed. Around five regiments (~4,000) will be going in down the middle, with smaller three-regiment attacks (~2,500) on the flanks - while this is going in, the American artillery will deploy on a rise of ground to the north and begin bombardment of the main British line.