Without an ASB making the entire Rockies inaccessible and extending or being connected to Baja which is just as inaccessible there is no real POD which prevents the U.S. from claiming California and the west coast in the end. The geographic distances from the Old World powers in Europe make this practically guaranteed.
Couldn't the same have been said about Canada as a whole though? This sparsely spread nation populated with a similar stock that stretched right from the atlantic to pacific seemed ripe for the taking for the USA but the threat of conflict with Great Britain always held them back.
If Britain had really laid a claim to the pacific coast it would be a while I think before the US could challenge that.