Is there any difference between a track made from 2oz copper, or one plated to 2oz
Any time you're plating, you're not going to have the same strength as you would get with a solid piece of copper. With that said, when delamination occurs, the void usually occurs within the insulator, not at the plating surface.

Why are you considering building up to 2oz with plating instead of just going straight for 2oz? Is this an attempt to precisely control the thickness?