I’m certainly no expert in print media, so take what I say with a grain of salt, but…
No, pixels don’t correspond directly to inches because a pixel isn’t a unit of distance/length. Inches are of a static length, whereas a pixel can be different lengths depending on the context (size of screen, desired resolution, etc).
However, I think for your purposes, the main thing you need to worry about is just the ratio – as long as your custom sizing in pixels has the same ratio (2x3), your page designer canvas will be the same “shape” as the labels you want to print. After that, I’m sure there is some number of minimum pixels you’ll want to hit in order to get good print resolution – I feel like I remember seeing numbers like 300ppi and 220ppi (where ppi = pixels per inch). So aiming for something like 600 x 900 pixels should meet your needs.
Again, I am speaking of things with which I have no real experience, so I could be off – but that should get you moving in the right direction at least.
