How to resize multiple stickies to the same size

In addition to @Kiron Bondale’s perfectly correct answer, you can select them, then drag a corner of the selection to make them all smaller or larger compared to how they are. So for instance if you wanted a bunch of different sized stickies to all be the same size, twice as large as the L preset, then you can do what Kiron says above, then drag the corner to make them all larger together.

@gregory fischer - You could take one of the stickies that you want to match the size of, then select your other group of stickies that you want resize, use the auto-layout tool to align them, drag them beside your target sticky until the tops are horizontally aligned, and then drag the group of stickies until the bottoms are aligned too. And because all of that was likely too much to just magically visualize in your head, here is an example:

You can use the switch type action:

In action: