Hi. First let me apologize for not directly answering your question(s). I don't entirely understand your description or your picture. However, I do have a pretty good grasp of flow, so I will make a recommendation based on your objective. I'm going to assume you've read the wiki on pressure, flow, pumps, etc and so I'll try not to just repeat the info from there.
I'd recommend forgetting about pumps. Pumps cause pressure, and pressure kills flow. You're better off letting gravity and obstacles do all the work. Don't just use a few obstacles, use a lot. Most designs seem to like a few blocks across a channel - for a channel n tiles wide, yielding n-1 flow points - but I've found that to be too few to really get water flowing. Instead, dig a channel four tiles wide with the center two alternating blocks and you can make as many flow points as you want, depending on space. With one side pressured and the other not, you might be surprised how fast water fills an area with ten flow points. The unpressured side can be open and should be able to support all the water wheels you want.
The part I didn't catch is what you plan to do for an exit, and that's the most important part. If you're not providing an exit at all, then flow will be very difficult if not impossible. If you can get your water to a map edge then flow will just happen. If you can drain it into an aquifer or a cavern lake then it should work fine as well. If you're trying to pump it back up into the river or loop it back into the canal again, then it can be tricky. I've made it work and also failed to make it work - I think it's a matter of tweaking volume control. I've never tried a 'portable hole', but I'd bet that would be a way to get flow in your canal as well.
As for fish, I have no clue. I don't recall ever getting vermin fish in my artificial canals, but I also didn't really pay attention. The consensus of a quick search seems to be what Patrik said - either the area will support them or it won't.
Hope that helps, good luck!