Hi Xan. Check your Rulebook(I do not own this one),but you will probably find you can attack over the Canal. (In  all the A&A games I have,  you can do.)
It is Naval movement that is stopped if you do not own both sides.

Oh my. THAT changes things. I just checked the PDF version of the manual, and you are right.

That drastically changes several (previously) working strategies. Oh man, my buddies are going to hate my guts when I pull this out on them. I’m tempted to give them a heads up, just so the game isn’t won by that rule change alone… but the looks on their faces will be so priceless, I just can’t warn them. :evil: