How to customise variations

how can I remove a specific variation selection.

My product has the option to add a canvas or no canvas, when I’m setting the variations for a product, I am unable to deselect the canvas option with the sizes. Is there any way I can only chose sizes without canvas variation?

Example: Product one:

canvas + Size

Size

Canvas + size + frame

frame + size

Is there any plugin, shortcode or somewhere i should look at, been trying to research it for 2 days haven’t found anything.

Thank you in advance