Many moons ago I used to fish for pike in the Union Canal with the fly. Never caught anything of any size but there were plenty of jacks. Now that the canal has been opened up for navigation the water is very coloured and the weed beds have died right back. I've not fished it since its been in this state but I would imagine that fish are still there. Best bits used to be the Basin at Fountainbridge along to Polwarth, the back of Harrison Park(s) and the area around the Aquadauct & Viaduct at Slateford. The back of Meggetland was never one of the best spots. I walked along the tow path a couple of weeks ago and noticed that they had been dredging this whole stretch so that will have impacted on the fishing
I don't know what its like now but Bonaly reservoir (steep but pleasant walk from the carpark at Bonaly) used to be stuffed full of pike. Other spots to think about are the quarries out in west lothian at Winchburgh (clayhole) and Humbie - the canal out there is also quite good. Duddingston and Dunsapie both have pike in them not sure about access though.
Norm