Man, that does bring back memories. I remember reading those arguments and feeling simultaneously entertained and incredibly annoyed. I never even bothered to read BROS because of the author's attitude in those arguments, I can only imagine how that TL reads like.
Canadian British Alaska I did forget how... opposed the Russian Empire was to the British. I'm rather curious then if the Americans don't buy it then who are the other potential buyers? It can't be the Japanese, they're still pre-Meiji and under the Tokugawa Shogunate and I don't think they would have the capability to support an Alaskan colony. Neither Prussia or Austria would have any interest or even capacity at this point. I don't see France being interested, besides they've got their Mexican project ongoing. So who does that leave? Only candidates I can think of will be either Meiji Japan (if the restoration hasn't been butterflied) or less likely post-1871 Germany.