Just wanted to share how I download my designs from Canva with 300 DPI.
When downloading my image, I save it as PNG with a maximum Size of 3.125.
After that I always open the PNG file in Paint (on PC) and go File - Image Properties to check the resolution.
If the PNG file is too big (more than 20 MB for Etsy), I resize it in Paint (Resize and Skew button) by reducing the Pixels untill my file is 20 MB or less. This does not change the DPI. So all my designs are 300 DPI or more, because that's what I promise my customers.
Same trick can be used if you are using Kittl and the AI upscaled image is too big. You can reduce your design's size in Paint without loosing the 300 DPI resolution before uploading to Etsy.
Happy designing!