Never fished the Forth canal, but I would concur with hunter and Michael Dodd - Single or double maggot (try different colours to see what the fish like, I've sometimes found them going for plain ones but leaving the smokey bac.... I mean bronze maggots alone) fished on the drop with most if not all the weight directly under the float.
Try putting a few maggots into some water for a few minutes, not enough to immerse them but just enough so that they are about half submerged. You should find that they take in air and will then float above the canal bottom when you cast in (you will have to use a small shot to anchor the line on the bottom, otherwise they will just stay on the surface).
With spring just around the corner, use small amounts of groundbait and/or loosefeed (I would cut loosefeed out almost entirely now), and I would put something like Whizzo Fizzyfeed into the mix if nothing was happening after an hour or so.
You can also try changing the hook for a smaller one, and if you don't do so already, try using hi-tech line or braid as a hooklength instead of normal line. It's much more supple and gives the bait a more natural look (apparently).
This is pretty obvious, but canals are noted for having little in the way of "features". However, if you can find an overhanging tree or bush, or some submerged plants, you may find fish congregating underneath.
If all that fails, stand up and walk a few yards down the bank and try again. If the fish aren't there, you ain't gonna catch....
Tight lines