on the Wolfs this is mounted to the role cage, as already stated.
the Wolfs dont actually use canvas, so if you wanted a bona fide 'wolf' you would need a PVC 'canvas' tilt, the wolf ones have all the necessary holes for spare wheel mount, ffr aerial etc. They usually go for about £400 so they arnt cheap but are much nicer than canvas in my opinion.
Im not sure how you would fit it to the cage, but you would need the carrier 'hub' and the trapeziod shaped backing plate for the mount itself.
I can't comment of whether the actual Wolf cages have mounting plates for the carrier but if you have a 'non' wolf cage i would guess you would need to drill and bolt it, ideally weld it on, and if necessarry re-enforce with some steel structures
if you are sticking with canvas, yes, you would have to cut your canvas