The Christopher Plummer stamp was issued as a booklet pane of self adhesive die cut stamps. The booklet is 3303a, and a single from the booklet pane is 3303. They also issued a pane of 6, with water based gum and perforated. The pane of 6 is 3302, and a single from the pane 3302a.
They did the same with the Heroes of Winnipeg's Valor Road: Booklet 3306a, single from booklet 3306, pane of 5 3305 and single from the pane 3305a.
Look at the perforations. If they have been die cut, they are from the booklets. If they have been torn apart, they are from the panes. BTW the booklet stamps are much more common.