Ps Towpath etiquette > slow down when passing for everyone, even the ignorant!
A very good point. Assume that everyone else has "priority", smile and greet them with a friendly hello. You ride might take a few minutes longer but it will be a whole heck of a lot better for it.
My son has a Sirrus, just the base model which ships with 32mm tyres, and he takes that on towpaths regularly - in fact, the trip home from the bike shop collecting it was along the Thames Path. Depending on the tyres you have, slippery mud will be the only thing I'd countenance against, and you might think about switching to a 32mm CX-style tyre if you are going to hit the canal regularly. CX-style tyres generally have a smooth mid-section, so they won't slow you too much on the tarmac, but they have blocky edges so they can cut into the gloop if they start to sink or if the bike gets away from the vertical.
In the dry, a Sirrus will handle just about anything on a towpath just, maybe, a touch slower than something with suspension and dedicated off-road tyres.