The best scenario for alternative Canada is where BNA gets all land north of Ohio River as part of the ARW. The French snd Spanish did not want a supercharged USA. Their interest had been only to weaken Britain. So have the British, French, Dutch and Spanish all agree that US size become curtailed.
1) BNA get all land north of Ohio River.
2) Spain and France get same territory as iotl.
Britain with huge BNA offers all to buy out loyalist property in USA and help pay their move to BNA. Instead of 75,000 BNA gets 175,000 loyalist.
USA and Britain are trading nations but not buddy buddies as iotl.
Investment by British firms and investors in BNA. Large track of lands sold for little $ to British citizens who agree to settle in BNA.
Catholics given same rights as Protestants in BNA.
From 1790-1810 several canals and locks built along st Lawrence and great lakes so that direct access to all lakes possible by ocean going ships.
Peace established with natives who get 20% of all lands and provide BNA troops with auxiliary support against American intrusions.
Americans allowed to settle in BNA in small scattered groups mixed in with British, Irish, German and French Canadians.
Limited skirmishes between British/natives and Americans as they spread out west of Appalachia mountains and south of Ohio River.
When British hear that Napoleon going to sell French Louisiana they order Troops in BNA to seize it. British navy shells and captures New Orleans.
War of 1812-14 results in America not able to dislodge British troops from occupied territory although New Orleans is destroyed in fighting.
Peace treaty between US and Britain divided French Louisiana with all lands south of St. Louis belonging to USA. New Orleans becomes international city guaranteeing british right to navigate the Mississipi.
Following napoleonic wars British offers thousands to veterans large tracts of land in BNA if they move there. From 1815-1850 BNA population grows 4 fold. in size.
With St. Louis and all lands around it under British control less than 20% of Americans able to make trek to west coast. British claim all land now part of Washington and Oregon.
USA fights Mexico and gains Texas, Santa Fe snd California.
In 1850s British seize Russian Alaska during Crimea war.
1860 BNA unites as kingdom of Canada with Queen Victoria second son as Canada’s first king.