Manhattan doesn’t have much room to expand up or out but but Seattle still has 70% single family homes it and surrounding cities have plenty of room to build up.

Spokane is largely populated by bigots and Trumpers. In particular the state congressman they elected wrote a paper the “biblical basis for war” wherein he advocated that after the fall of the united states they would make war on the rest of us nonbelievers taking the women prisoners and killing men who wouldn’t submit in his new Christofascist white ISIS like kingdom. He was then caught trying to “rescue” a bunch of Ukrainian kids on behalf of an organization that existed on paper only without doing boring stuff like making sure they didn’t have parents fighting in the war or other relations who wanted to take them.

On an economic front the Seattle Metro area has substantial commerce, an international airport, a port and 4M people. Spokane has about 230k. Adding another 230k would be a 5% increase in population for the Seattle Metro it would double spokane. The resources for expanding housing and resources in the Seattle metro actually exist. If it ever makes it there that is about half a century of growth for Spokane.