Now that I have seen your example, I return to my original suggestion of Designfera's Cracks brush in the Marketplace.  I tested it on one of my paintings, using brushes with full image cracks (3), one of which has a shadow effect with could be used for 3D effect with an emboss filter.

I used a new layer, reduced the size to approximate what you show in your example, then duplicated the layer enough times to cover the painting.  After positioning each crack layer, I merged them, and tired composite blend and/or reduced opacity.

Also, if you wanted some areas without cracks, you can erase sections from your merged layer, giving an uneven cracked canvas.  Remember to save the image before you start erasing, so you don't get stuck without a way to get the original crack layer back if you make a mistake erasing.

Hope this helps.  I really don't have any other suggestin that would be as good as the one above.

Best wishes,
Suzanne

“Music is harmony, harmony is perfection, perfection is our dream, and our dream is heaven”
Henri Frederic Amiel