I'd say that image (of the leg coverings) points to suede not canvas.
I'm not entirely sure that's accurate. Though there does appear to be a rough texture to them in the above pictures, if you look closely particularly around the tops where the buttons are you can see that it's smoother. I think the texture is from severe distressing and weathering applied to them.
The pattern of them is consistent with US WWII canvas infantry leggings, apart from the leather straps added under the boot bottoms (which would have been webbing on originals) and the button fastenings (which would have been eyelets and grommets for lacing up).
I still reckon they're canvas... made in the WWII pattern, but with buttons substituted for closure. The buttons themselves look rather like the buttons used on WWI and WWII "half shelter" pup tents.
There may have been a country who issued leggings of this sort as is... though usually leggings lace up in order to avoid having to have so many different sizes available for different legs. They may be a found item... but they may also have been custom made using an established pattern and substituting the buttons.
In any case, I believe a very SA result could be achieved by copying a WWII US infantrymans' leggings and substituting button closure and leather under straps.
To me the original colour appears to be Khaki, with either O.D. or brown acrylic paint dry brushed over the top of them to give them a soiled appearance.