The ornamental design for a cannister, as shown and described.
FIG. 1 is an upper front perspective view of my new design;
FIG. 2 is a sectional view taken through line 2-2 of FIG. 3 thereof;
FIG. 3 is a front elevational view thereof;
FIG. 4 is a lower front perspective view thereof;
FIG. 5 is a top plan view thereof; and,
FIG. 6 is a bottom plan view thereof.
The even-dash broken lines are for the purpose of illustrating portions of the cannister and form no part of the claimed design. The long-dash short-dash lines show the section cut and form no part of the claimed design. Any broken lines showing the interior portions of the cannister in FIG. 2 depict unclaimed structure and form no part of the claim.