Very well done, H-R and AR. Those maps of yours are things of beauty. As it concerns the internal borders of the bicontinental US, yes, there are several cases where they shall be different (e.g. the borders of ex-Canadian ones are already rather different). You all know that this is a task I take up reluctantly, necessary as it may be. So far, I've strived to puzzle out where and how the borders of those states would turn up really different, giving shorthard descriptions in the various US updates. As to putting them in a map... we shall see, since as you know my map-making skills are limited. I could try to create a rough scheme, which our resident map-makers could refine. We shall see in the future. I'm as yet more than a bit uncertain when and how often this would be worth to do, since surely I don't want to tackle the task for every statehood.
Aranfan, this USA shall indeed cast off isolationism a lot sooner than OTL, but at least until sometime between ACW and the first global conflict I do not see exceeding reasons for themselves to get embroiled in the European alliance system. Surely they have their ongoing imperial rivalry with the British Empire, first in South America and then in the Pacific, and this shall motivate them to seek an alliance with the Eastern powers sooner or later, but I'm not yet sure when. If Britain and France try to interfere in the ACW (a big if), it could be as early as the Reconstruction.
K-H, basically, the US expansion in most of what is the British Empire (BSA, Anzus, South Africa) shall occur as the result of the ongoing imperial competition with the British Empire, and because this USA has got Manifest Destiny ideology as an integral component of their national identity. They look towards all of the Americas, and the extra-American British colonies that loosely resemble the USA socially and culturally (e.g. Australia, New Zealand, South Africa), as potential parts of the USA waiting to happen. Since they do not see themselves as aggressive, they do not go out of their way to start wars and annex them, but once a war does happen for whatever casus belli triggered by expansionism and imperial rivalry, bets and gloves are off and they deem the only fitting outcome for those lands is to become American if they can conquer them at all. Typically this means a period while conquered lands stay US territories/protectorates, while they are settled if scarcely populated, the territory is made socially, politically, and economically fit to be a US state (and America works out whatever racist kinks it may still have to give statehood to bunch of colored backward folks), and the conquered peoples realize that the Americans are fully determined and able to stay and keep all of what they conquered, the only way out of permanent US military occupation and subject status is to accept their own destiny as Yankees and embrace US statehood.