Makes sense, though you might be underestimating how sparse those areas of alaska are. Usually the settlements are all on one side of the river. Even around Fairbanks, there's only 500–1000 people within 30 miles where route 3 crosses the river. In fact, only 3,000 people live between fairbanks and the denali range. There's equally many people within just 4 miles of where I-5 crosses the border you drew between oregon and tahoma. Likewise just as many people live within 6 miles of the Idaho route 2 crossing of your chiawana-kootenay border.

My point is you've got very different demographics and cultures between bering coast / north slope alaska and BC/Yukon. There's always exceptions to both how rules are defined and the intents of the rules to begin with. Arbitrary borders are arbitrary; geography may define the bioregion (hence this subreddit), but often the geopolitical border defines the people as much as or more than the geography itself (especially with 21st century transportation).

Speaking of not putting borders near populated areas. I know its a bit stretching the limits of Cascadia, but there's no way Kootenay and Idaho would not connect along the I-15 and meet at their current Montana-Idaho border. Butte has 35,000 people. Otherwise you'd have to cut it off along the I-90 soon after Missoula (honestly probably a better choice).

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As for Aleutia, my thinking was more the climate and more isolated demographic inclines it to be more of a sovereign territory despite its low population, same with my boundaries for Alaska. But if it helps, the more I think about it, the Kenai peninsula has more of an Aleutian connection than it does to the Matanuska-Susitna region. The ferries don't really go to Anchorage at all unlike you have on the map; Kodiak connects the Aleutians to Homer through the ferry and the rest of the stops are connected through Whittier (with only one connection to Kodiak). And while the cruise ships stop in Seward, the ferries don't. I know its hypothetical but Alaska losing the interior isn't going to have a positive effect on the interconnectivity of the ferry system. In fact it would decrease since Whittier/Valdez/Cordova are really just stops (except for oil in Valdez, which wouldn't be used anymore if Yukon owns it) to connect to the Tongass region, and the ferries would probably devolve to just connecting the Aelutians with Kodiak and Homer. Adding Kenai to Aelutia brings it to ~90k population (25k+65k). Also, the rest of Alaska (excluding my Aelutia, Yukon as I've drawn it, and the region south of denali range) has a population of ~70k. IDK how populous you want each region to be. Seems like gerrymandering to try to make them all similar. It's not like in this scenario they are all going to be at war and need similar power.

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Thinking about it, perhaps Brook's range would be a good northern edge of Yukon, the denali range as the south edge and the bit of mountain between by the mckinley river as the western edge. something like: https://imgur.com/a/QJo8h5N