Yes! I was able to resize the canvas. Documenting my experience for future reference:
The "target" widget is the canvas, like you said, and the "Export" button checks its size to see how large it should render the .GIF.
The "dims" widget behind it is the canvas size that the other buttons refer to, namely "Obliterate" and "Oops!". I was having an issue where clicking "Oops!" would resize the canvas to the original WigglyPaint resolution, but I found that resizing the "dims" widget to the desired resolution made it so the canvas would reset to that size when I clicked on either of those buttons. The "Crop" button/menu is probably defunct now.
Lastly, because I resized the entire deck, I had to move the buttons and brushes to accommodate the new canvas. The buttons at the bottom (excluding "Options") are half attached to the canvas itself, so I drew new visuals to account for their new position.
Thanks for your help!