Hi there,
Yes the Corran ferry is free to foot passengers and cycles.It's minutes from the site at Bunree.If you turn right when you come off the ferry,the road runs in the same direction as the main road going to Fort William.Wouldn't suggest trying the A82 into F/William as it is a busy twisty road.
Not sure what standard of cyclists you are but my hubby & his pal cycled the tow path recently at Neptunes Staircase.
Drive to Fort William and then take the A830.Before reaching Corpach there is a sign post to the right ( B8004 ) to Gairlochy.Take this and you will see a large car park right beside the Neptune's steps.There is also a hotel "The Moorings".
From here you can cycle the tow path for 7 miles.At Gairlochy there are NO facilities so take food with you.When you reach Gairlochy you can go through a gate and there is a little light house where you have a view right up Loch Lochy and you can sit & have your sandwiches.It is quite a busy canal with boat activity to watch as well.
Do you also know about the steam train from Fort William to Mallaig?