An independent Scotland or Wales would have pretty much the same trading relationship with the EU, as England has.

At least for several decades after independence

The level of integration of everything, including trade and supply chains and finance etc, is so big as to be almost total.

In addition, I'm pretty sure that EU would not welcome another hard border with England, it's already waisted far too much time and effort on the issue in Ireland. I'm sure it doesn't want to have to go through that again.