"just" install vertical pairs of rails along both side of the canals. top rails goes south. bottom rails goes north. Pulling engine attached to the rail. Have a rule that the bottom rail tethered ship disconnects before crossing incoming vessels. The crew then reconnects to the trucks after passing. Make sure the cable are high enough that other ship can pass under. Or both ships disconnect. Or top rails ship has an arm that lift the slacked cables during the crossing, and the bottom rail ship has an arm that dunks the other cable bellow the incoming ship during the passing.

Rail or battery rail powered rail cars (basically an engine and a hooking system) on the rails pull the ship, positioned on the canal.

The rail trucks can have big V shape receivers for the crew to throw the tether ends to reconnect without having to stop and come ashore.

Of courses you then have to look at the cost and general burden of installing all this infrastructure, maintaining it, ensuring the safety of having the trucks not crushing anything, making sure the boat arms can ensure trouble free crossing.

But yay, you save a lot of fuel and it might be more efficient than the boats propelling themselves.