I've got a Makita DUC254 and it is brilliant. 18v battery. It is a light top handle saw with a 10 inch bar and direct drive so very high chain speed. It will bog down if pushed and the battery does not last long. Last winter full time residential ( I only go out for shopping and short walks) with no other heating I only burnt 5 bags of coal mostly because of the Makita.
It's great.
If you want to do larger stuff the Makita DUC357 may be better. Reduction gear and a 14 inch bar give it a lot more torque.
The little top handle saw is not for people who want to push. I have done 15 inch cuts with it but only two per battery (5Ah) and you have to let the weight of the machine do the work plus the chain must be well sharpened.
It will not forgive a dull chain.
THE 36V Makita saws get good reviews. Not cheap but at the end of the day Makita do know how to make cordless power tools they have been doing it well for a long time.
I would be cautious about assuming you are authorised to cut live vegetation on the towpath. You may think it is causing a problem but it's not your land therefore you are unlikely to be authorised to do this. Also operating a chainsaw on public access land may be complicated by insurance requirements.
Canal towpaths are public access land.