Make a print-ready master
Add resolution to a small image for larger prints. Then make your print sizes in Size Packs, Perfect Fit or My Packs.

Example · enlarged as is

After AI Upscale
A print-ready master
One large image in your artwork's own shape.
File: JPG · 300 DPI
Maximum print size: 24×36 in / A1
Then make your Etsy sizes from it in Size Packs. How large depends on your file.