Both Adversary effects remove the "Coastal Lands” card before randomizing the Stage II Invader Cards – "Untapped Salt Deposits" just doesn’t do anything special with it afterwards, while "Seize Opportunity" puts it back in a specific spot.
Whether a land is Coastal is defined by whether the land is adjacent to the Ocean. Open the Ways can create an adjacency between two of Finder's lands, allowing it to make lands (temporarily) Coastal.