@Márton: Before 1.31 there is no effect to disable canals directly. You could only fully remove the great project and then start building it again. Since 1.31 there is an effect to add and remove the canal. However that is globally for everyone, you can't block it for specific nations.

For example that an embargo would have the same effect like being at war when it comes to canals

I tried to find a command to remove the canal but couldn't. When at war, enemies can't pass it. Do you think I could use this mechanic somehow and in which folder I can find it?

@Márton: No, because canals worked differently back then.

Is it possible to create a 1.30 version?