Yea if you're going for a canal of some type it can definitely take a lot of time to make sure a karve can get through without trouble. The Longboat requires even more finesse when it comes to width and depth. Might be just better to break down your boat and build it across the way and if needed make a cart to move supplies as it's easier to make a level road.

But hey if you just want to make a canal, go for it. Just make sure you have decent stamina food and a nearby fire hut for the rested bonus. Also a hoe just in case you have to raise terrain to get to a spot that you missed.