I cycled part of it a couple of years ago. I thought it was quite nice. Nothing too exciting, but a mixture of gravel paths and forest tracks etc, with a few bits on minor roads. Plus a few steep hills up and down. Plenty of nice scenery and good views over Loch Ness. Quite similar to the Great Glen Way, but not as busy.
Part of it is mapped on OpenStreetMap, so you could get a GPX from that. Most of it is fairly well signposted anyway. Plus you can download and print out maps from the official website, so shouldn’t be too hard to follow.
Note the route starts at Loch Tarff, so you’d have to cycle on the road for a few miles up from Fort Augustus. There is plans for a new path along this section, but I don’t think that has happened yet.