This TL idea is the combination of two different PoDs, which together expand significantly the boundaries of the continental USA northward and southward.
1) During the negotations between Britain and the Americans at the close of the ARW, there are somewhat less delays and interference caused by French and Spanish dickering at the negotiations table. As a result, the US still fails to claim the Maritimes and what shall later become Lower Canada and Quebec IOTL, but successfully asserts a claim to all the parts of the Province of Quebec that lie west of the Ottawa River and drain in the Atlantic, effectively the ATL equivalent of what shall later become Upper Canada IOTL. The northwestern boundary is placed along a line going westward from the northern shore of Lake Nipigon to the Mississippi River (due to the use of a faulty map, the diplomats fail to realize that the river did not extend that far north, as IOTL; this mistake shall be acknowledged in following decades and need to be corrected later, as it was in 1818 OTL). The treaty also establishes joint ownership of Rupert's Land, with freedom of navigation and settlement for both parties throughout, and a lease of the area to the Hudson's Bay Company, for 99 years. Afterwards, the ownership of the area shall default to America.
It is assumed that PoD 1 does not butterfly away the Mexican-American War nor changes its outcome.
2) When the OTL short-lived Republic of Rio Grande (formed of the Mexican states of Coahuila, Tamaulipas, and Nuevo Leon) secedes from Mexico in 1840, it does not pick a territorial quarrel with Texas. As a result, Texas and the USA support the republic and Rio Grande effectively defends its independence against Mexico. Later it successfully applies for US statehood like Texas and this triggers the ATL Mexican-American War, which still turns out in a total US victory. At the peace table, the US government is obviously interested in claiming the rest of northern Mexico and extend the Rio Grande border to the Pacific, so they claim the mexican states of Chihuahua, Sonora, Sinaloa, Durango, and all of Baja California. Since these areas are still relatively unpopulated at the time of the cession, claiming northern Mexico does not draw the racist concerns from Southern Democrats about incorporating a large mixed-race population that annexing all of Mexico would have, so the treaty is ratified.
In the OP's opinion, neither PoD is significantly likely and able to butterfly the ACW away or change its outcome.
What are the social, political, economic, and military effects of these PoDs on Canada, Mexico, and the USA ? Does PoD 1 butterfly away the War of 1812 entirely, or change its outcome ? Do US and the UK become even more friendly, or more antagonistic, in the long run, with a shrunken Canada ? How is ownership of Rupert's Land and Oregon Country eventually settled ? Does it make all of OTL Western Canada a part of the USA, or just moves the western US-BNA border northward, say at the 51st parallel ? How would Canada and Mexico fare without northern Mexico, the "useful" portions of Ontario and Western Canada, and perhaps without the latter at all ? How this would change the demographic and economics, and the state boundaries, in the USA ? Is the ACW accelerated ?