I'm too late now, but for the benefit of others in the future, here's what I have found.
A couple of months back, I went from Edinburgh to the Falkirk wheel. I decided to get there on the canal path. It is excellent until you are outside Edinburgh, after which it is truly a nightmare. Note that I took my MTB not my roadie, because I suspected the path wasn't going to be smooth. And it wasn't. It was also littered with people and dogs, and the path was so thin, you couldn't get past them. Also, you cannot go more than 10mph ever, and even when you got to that pace, you had to slow down again (for people and dogs, which is fair enough, but the thinness of the path just slows you down). Frustrating, and arse painful due to the surface.
I came back on the roads. Fractionally less distance, and vastly faster. I took the direct route - Falkirk, Linlithgow, Winchburgh, Kirkliston, Cramond. I think it was the a803 and b9080 mainly.
I will never again take the canal west of gogarburn on a bike. Good for running, though.