A northerly route across the Canadian prairies (Winnipeg-Vancouver or something similar) is reasonable enough and likely gets built eventually, but the Canadian Shield in northern Ontario is remote from major population centers and difficult to build on, meaning that in the absence of a border between Canada and the US there's no reason for any transcontinental railroad to route north of the Great Lakes. Any rail connection between Montreal and Vancouver most likely routes south through Toronto, Detroit, and Chicago rather than taking anything resembling a straight shot west.
Such a purchase might be made significantly earlier, as part of TTL's Oregon Treaty. I will also note that the districts you are using as the basis of states in the Alberta-Saskatchewan region were never districts of the Hudson's Bay Company. They were first formed in the 1880s and did not achieve their depicted boundaries until the 1890s, well after Canada acquired the Northwest Territories in 1870. The more northerly ones would also be rather thinly populated if admitted as states: there's a reason Canada decided to consolidate them into two provinces instead of admitting them as four.
As to the boundaries, the general thing to note is that by adding four more northern states to the Union right from the beginning, you have significantly altered the balance between free and slave states, which will have important ramifications for US foreign and domestic policy, as well as US state boundaries.
You also have a lot of common AH state borders going on: West Florida, MegaWisconsin with Chicago and the Upper Peninsula, Texas with the borders it had as a Mexican territory, Vancouver Island separate from British Columbia, SoCal separate from NorCal, not just one but
two states of Jefferson (
Mountain and
Pacific), 1890s borders in the Prairie Provinces, and the US gaining Baja California from Mexico but not the Gadsden Purchase or the Nueces Strip. These aren't bad things per se (although the 1890 Prairie Province borders are definitely way too convergent, especially given how different all of the states in the surrounding regions are), but you should make sure you have a decent sense of how and why they came about as a result of your POD and its consequences, and that you aren't just throwing in a bunch of differences from OTL without thinking about how they go together.
Now, some additional notes:
- I don't see how or why you have a separate Plymouth. Your POD is around eighty years after your last easy chance to save it around 1690, and to the best of my knowledge there was never any serious desire to carve it off as its own state post-ARW. I'm not sure what your POD would do to change this, and the Southern states would fight it tooth and nail.
- While I can see Illinois having a more southerly northern border than IOTL, I can't see it being denied access to Lake Michigan as your map seems to, especially given the relatively minor border adjustment that would be needed to give it lake access. Sea/lake access was an important consideration in drawing state lines IOTL, and I don't see why it would be abandoned here.
- Relatedly, IOTL the major concern when dividing the Missisippi Territory into Mississippi and Alabama was creating two equally sized states with sea access. Although a partition into three states is understandable given a desire by the South to admit more slave states to balance out the North, a partition into three quite unequally-sized states with only one having sea access seems unlikely to me. A single state of West Florida would make much more sense than having a narrow southern one that controls the coast and a larger northern one that is completely landlocked, and if it must be divided into two it would make more sense to go east-west as IOTL rather than north-south. (I would also consider shrinking North Mississippi-Alabama here by moving West Florida's borders further north and/or Tennessee's further south.)
- I would recommend against splitting New Mexico along the Rio Grande. The deserts and mountains on either side of the river are more significant natural borders than the river itself, which forms the state's major population center: it was always administered as one unit IOTL, under Spain, Mexico, and the US, and I'm not sure why America ITTL would feel differently.
- It is curious that your US owns Baja Calfornia even though its border with Mexico is otherwise consistently further north than IOTL. I think it could probably be justified with the right explanation, but you should have a sense of why things shook out that way.
- Some of your states are a bit small or sparsely populated, especially historically: I've already mentioned the way you handled the Prairie Provinces, but having, say, two separate states in northern Ontario is a bit surprising. Again, not implausible per se (Nevada IOTL didn't even break 100,000 people until 1940), but you should have a sense of why the decision was made to draw the boundaries that way.
