Do canals affect land value

First, a few tips:

1. Go through every information layout possible and make sure your citizens are covered by all of the necessary services
2. Check your building levels for Residental, Commercial, Industrial/Office and try and get them up as high as possible
3. Traffic can make or break your simulation. I recommend using the "Traffic Report Tool" mod to help wrap your head around why a citizen is going where (it might help you spot missing road links!)

I am currently having your exact problem. My current has 131k population but zero demand:

As you can see my RCI is almost zero across the board. Something else must be going on here. My traffic has hardly any red spots, tons of services, and high land value in the right places. What's going on? It turns out high unemployment can cause your city to be undesirable to move in to:

But how do I have unemployment if my industry demand is zero? Personally, I have an un-even location placement of homes vs jobs.

I think this is causing my high unemployment even though there is no demand for OVERALL RCI. The industries that are far away from homes are complaining no workers are available while the residents that are far from jobs are left unemployed.

I also have a few other problems like an unnaturally low commercial percentage thanks to the park bug (BTW, thanks for the mod heads-up, I'll check it out!)

The general plan with the use of larger vs. smaller roads, mimicking real life road planning, is to create a "hierarchy" of roads. See this guide for general ideas on planning road networks. With this in mind, the larger four and six lane roads serve as the "trunks" to two lane road "branches". These larger roads handle a higher volume of traffic at higher speeds, allowing users to reach the point of their "branch" which will take them to their ultimate destination (though these "trunk" roads can also have things built on them, like commercial buildings, which like the customer flow of the larger roads).

As far as two way vs. one way is the concerned, there are two things to consider:

1) Bottlenecks. Trying to force the traffic to take certain, pre-planned one way routes can backfire big time if you're not providing enough different ways for the AI to get to its destination. This is a big cause of the infamous "every car is pilled into one lane" problem people complain about. They're doing that because they're all trying to turn the same way at the next light.

2) Services. A complex maze of one ways is difficult to navigate, and can cause major delays in service response time. Remember that service vehicles in this game have no "right of way", they have to follow all the same traffic rules as everyone else. Because of this, a building might burn down even though there's a fire station directly next door, but next door the wrong way on a one way, causing the fire engine to have to drive all the way around the block.

For your screenshot, two suggestions:

1) As far as I can see, there's only that one entrance and exit from your industrial area. This is a bottleneck, and can be alleviated by giving the traffic more options, either through adding more road connections, or other transport options, like freight trains.

2) The intersection of the the highway and the six-lane is very close to another intersection of the six-lane with another six-lane. The "stop, start, stop, start" from those intersections can jam up traffic. Try giving your traffic coming off the highway some "run-up" time before it encounters a traffic light.