U.S. bound from Windsor to Detroit the Ambassador bridge nexus lane is impossible for anything but a car ,it is a squeeze for a large pick up.
There is a very tight double turn after the customs booth before the toll shack,a small class C maybe .
This will hopefully change in the next few years after the new bridge is complete.
I have never seen the tunnel nexus lane ,but the tunnel is through downtown (both sides) and does not bare thinking about.
I see the OP is from Burlington ,maybe someone can describe the Sarnia crossing ,it is closer for you anyway.