I have this in leather. It is a great bag, love it. Very confortable, very practical. It is not heavy at all.
I was also considering it in canvas for the Summer, but went with a basket instead, and I have the Dior Book Tote that would serve an similar purposes. The canvas is durable and nice quality, but it stains easily. It is not coated, and not hard like say Hermes toile. The thing that bothers me the most is the bottom of the bag, I wish they’d make that in leather, as they do with (some of) the seasonal Cushion bags (check the de Morgan collection). I asked Loewe and they say they do not provide cleaning for these bags.
If you want to use the bag for carrying a laptop and stuff, do consider the Medium size. I find it more confortable to carry over the shoulder than the S size too. The L size is too bulky as the bottom is square.
Thanks a lot, very helpful!