A truck shipping parts made in Windsor and going over to Sterling Hgts or Warren, MI is not going to drive to Sarnia, cross at the Blue Water Bridge into Port Huron and then drive the 45mins down into Warren.
This is simply a case of Trump being Trump. If the Fed's can wait him out and not care about the bridge not being open for another 2,5yrs then just leave it closed. The state of Michigan will put more and more pressure on Trump to get it open before then. There is no pressing need, in terms of volume of traffic using the existing Ambassador Bridge or the Windsor-Detroit Tunnel that it can't wait him out.