What if we built a huge gulf basically down the plains just on the other side of the rocky's so basically there's a gulf splitting America into two completely b

What if we built a huge gulf basically down the plains just on the other side of the rocky's so basically there's a gulf splitting America into two completely by waters from the artic ocean or north pacific, I'm talking we dissect all the way north through canada all the way down through mexico etc. This would maybe create new weather patterns, in combination we'd need to plant LOTS of trees which also creates weather patterns to change, but we could terraform the utah desert to be more like the midwest, but it would be defense-budget costly to do so, but if it worked it could be worth it.