The ornamental design for a cannula, as shown and described.
FIG. 1 is a perspective view of an embodiment of a cannula embodying my new design;
FIG. 2 is a first side view of the cannula of FIG. 1;
FIG. 3 is a second side view of the cannula of FIG. 1;
FIG. 4 is a third view of the cannula of FIG. 1;
FIG. 5 is a fourth side view of the cannula of FIG. 1;
FIG. 6 is a top view of the cannula of FIG. 1; and,
FIG. 7 is a bottom view of the cannula of FIG. 1.
The broken line showing of parts of the drawings is included for the purpose of illustrating use and environment and forms no part of the claimed design.