Port Huron?
To do that they'd pretty much have to come through Chicago.
I would think most of the crude going to Sarnia would be through the Embridge pipeline. They just doubled capacity on it.
However a lot of freight passes through Detroit both by train and truck. Availability of trains will make a difference.
It isn't about crossings at Detroit, it's about A) a nation-wide shortage of locomotives and B) trains literally having to wait for an available slot, all over the US, but especially along lines coming out of Alberta and North Dakota.
Trains around here are running almost bumper-to-bumper.