Not sure of the difference between the two, but I would say that it might be a case of you get what you pay for.
I searched around for a new canvas and ended up buying one from http://www.busdepot.com" onclick="window.open(this.href);return false; in the US. Worked out that even with duty and shipping could buy their better quality one for lower price than the UK suppliers. I was very happy with it when it arrived (took a few weeks to ship) and got it fitted in an afternoon.
Cheers,
Si