Is there anyway the US can gain the port of San Francisco and achieve gaining northern California above the 37th parallel in 1803?
Nope. For the US to get all that territory at once, it would have to be bought from Spain. And I can't see Spain giving up almost half of their North American territory without a fight.
Since it was during the Napoleonic Wars, could the US side with France and have Napoleon more situated in Spain and Napoleon being more friendly to the US allow the US to buy off a Pacific port later?