lol those jobs don't rely on the Ambassador specifically, just rely on having a major crossing in the region.
The more efficient freeway connections on the Canadian side benefit American businesses using the crossing, it's not like their trips instantly end once they cross the border.
And as has already been said, it will result in significantly improved crossing capacity resulting in much shorter border wait times.
The benefits are indeed less for Michigan than Ontario, but I wouldn't say that the bridge has *no* benefit. The freeway-freeway connection is a big benefit for anyone crossing the border as it will cut a lot of travel time, especially combined with reduced wait times.
Plus Michigan is getting a bunch of free bridge reconstructions along I75 paid for by the Canadian government as a part of the project, and the neighbourhood that was demolished for it wasn't exactly an economically thriving community beforehand..
https://www.google.com/maps/@42.3003...7i13312!8i6656
I mean the bridge clearly wasn't a priority for the US, they were too cheap to even pay for their own border clearance facilities. The project is 100% financed by the Canadian government, and you would have to be pretty stupid to turn down free money (although Michigan did get pretty close because of Moroun's lobbying).