If you are going to get a backpack (and I would, I use one to cart my laptop etc around in) then I wouldn't get one in a canvas material.
I would get one in a very smooth material - like Knomo or Roka do (I just list those as examples of brands that do bags in the sort of material that I mean, not necessarily as any recommendation).
Otherwise, if you wear a heavyish canvas rucksack over, say a jersey dress or a wool cardigan, it will rub against it and ruin the fabric. Maybe not the first time you use it, but it will happen.
I speak from bitter experience (and now have a canvas rucksack lurking unused at home somewhere
).
And yes, I agree that whilst leather looks much better, it is heavy to start with and so add a laptop, water etc and it starts to feel very heavy indeed.