You can just make out the two circular strait/canal icons for Kiel and the straits in Denmark.
As for channels from what i have seen submarines cant pass them aswell.
It depends on the rules for the canal/strait. But generally straits are OK - subs can pass through submerged, though it doesn't prevent them being detected and attacked. But the canals are too shallow for subs to be submerged. See here where subs can't sneak through the Panama Canal:
Notice also that even though you have a neutral stance with the controller (USA) your transport convoys and warships can't pass through Panama. Suez on the other hand should remain fully open for neutral shipping, because of it's different treaty obligations, so Italy has no problems during the Ethiopia War, and is only blocked once it DoWs the Allies. The controller (UK) can only block shipping for countries it is directly at war with.
IIRC Turkey's treaties would block their straits to all shipping, even trade, belonging to belligerent countries, even when Turkey is not at war.