Canal journeys mixed terrain MTB or hybrid?

[Pat "5mph"]

Hi @JustJane and welcome to CC!
I second the above opinions about getting your gears fixed, practice on them, see how you feel after, without spending money on a new bike first.
However, there is much to be said about older, 5 speed bikes: fitted with suitable, not to skinny tyres, mudguards and a pannier rack, they make the ideal canal explorer.
With only one ring in the front, cleaning canal mud is much easier, thinking of changing gear won't give you anxiety
I love my 5 speed (mostly use only 2 of the gears), got it from a bike recycling shop years ago, don't know if they still make brand new ones.

 

[Alun]

Oh drats one last Q
My husband wants me to.train on the flat to get my fitness up for the ride big I think I'm better just using the canal as that's the conditions I will be using

I don't think it matters, if you are happy with the towpath stick with it. Just get those miles in, and some longer rides as well. 60 miles is quite a distance along a canal bank on a MTB, make sure your tyres are the correct pressure and on the day just go at your own pace. Good luck.