I'm not entirely sure where the angry denouncements come from, but will answer a few in my humble opinions
-1- Alaska was initially valuable as a furs and whaling place, and Kodiak Island was important in this. Over time of course, the trappers spread out Southwards as they depleted more Northern populations, then came the Klondike and the discovery of gold. Now, that might seem to indicate a huge reason for Russia to have the lower West coast, but it is also a huge reason for Britain to fight to keep them out/boot them out. A war over the Klondike could well explain the Alaskan border on this map.
-2- California is not linked by land to anywhere in particular, except of course Baja which is rather negligible. There are great mountains all around the place, and getting there from the East in OTL was a nightmare. Even Texas owning the territory on the map gives them no greater shot at California. In addition, California had its own population, and its own administrative history. Its not about to merge with Texas without being conquered, which is pretty much not going to happen.
Britain on the other hand has a great advantage - not so much the territorial contiguity from Oregon, as the access from the sea. In OTL, the USA gained control of California not because of the patrols penetrating from the East (which were late, beat up and had to fight their way in) but because of the marines landed from the sea. If Britain wants California, it is in a much better position to take it from the sea.
-3- Quebec would be more confusing but does not need to be impossible. No Seven Years War, and British penetration from the 13 colonies Westwards could well mean that when a war does happen it is the prize of the (Old) North-West that is important and Quebec can be by-passed
Best Regards
Grey Wolf