Could their have been the possibility of a European nation colonizing the Pacific northwest (Brit Columbia, Washington, Oregon) besides the Brits, or the Russians before the 1800s.
Spain explored the area around Vancouver Island in the mid-1700s and claimed the coast until the 1790s, so you could have some Spanish missions being founded there.
If Japan were friendlier, then the Manila Galleon could take advantage of the great circle route to Mexico, along with favourable currents and winds. The Pacific Northwest, then, could become a Spanish colony settled mainly by Filipinos, Japanese, and Mexicans.