The ornamental design for a footprintcanvas, as shown and described.
FIG. 1 is a perspective view of a footprint canvas showing my new design;
FIG. 2 is a front view thereof;
FIG. 3 is a top view thereof;
FIG. 4 is a bottom view thereof;
FIG. 5 is right side view thereof;
FIG. 6 is a left side view thereof;
FIG. 7 is a rear view thereof;
FIG. 8 is a perspective view showing the design prior to addition of a footprint; and,
FIG. 9 is a front view of FIG. 8.
The broken line showing of the footprint depicts environment and forms no part of the claimed design. The footprint is shown with an overlay to illustrate that the surface of the footprint within the broken lines forms no part of the claimed design.