The Detroit River, separating Detroit, Michigan and Windsor, Ontario, averages about 2,400 feet in width (731 meters). Not an overly taxing distance, if you were to decide to for some reason swim it. Maybe exhausting to the average person who doesn't swim much, but if you do any regular swimming at all, you'll be fine.
However, it is a rather bad idea to swim in the Detroit River. Let me explain why. First, the river is extensively used as a shipping channel servicing not only Detroit and Windsor, but it connects Lake Erie and Lake St. Clair, the latter of which is sandwiched between Erie and Huron. Other open-water swims are used by ships as well, they all are, but in the case of, say, the English Channel, there's room for everyone. A boat, a ferry, they can give you a wide berth if you're going to swim it, and generally when someone tries it, there's enough advance notice to all involved that they know you're out there. And there's almost certainly going to be a support boat chugging alongside them in case the swimmer can't make it across. In the Detroit River, there's no room to get out of the way. If you're in a boat's way, you're in their way. And a cargo ship is not a swimmer support boat. It is a cargo ship. A swimmer's going to lose that battle every time.
Second, the current in the river is about 1.5 times average velocity. That means, odds of bodkins, the river runs faster than your normal river. Doesn't matter how short the width is; if it sweeps you way off course, you're in trouble.
Third, swimming in a shipping channel is slightly illegal.
Fourth, they don't like it when you cross an international border in the process of doing something that you decided to do after... let's see here... "a night of drinking." It's never a good idea to swim across an international border while drunk. It is also never a good idea to do so twice. Boats and helicopters may be deployed to fish you out. The operators of those boats and helicopters will be unhappy.
Please do not make them unhappy.