Trade California for Canada and Greenland. Offer all Danes the right to emigrate to California as a sweetener.
We may have to throw in Oregon and Washington, but we should move the Northern border of Washington down as far as possible to get access to the ocean.
We may want to buy Baja California from Mexico as well to gain access to warm water.
Canada is 10 provinces + 3 territories.
But you are right - it has approximately the population of California (40 MM for Canada and 39 MM for Cali)
As to Greenland, it is not “owned” by Denmark, but is a separate country under the Danish crown.