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To enter the US under the visa waiver program by land, you don't actually need ESTA. Also, there's no need to "clarify you've left with your J-1 visa" because once you've left the US your J-1 status ends, and because you're in your grace period you are not eligible to re-enter in J-1 status.
But to answer your real question, yes, it is possible. There is a risk that you might not be admitted to the US, however.
You can also apply to remain in the US through a change of nonimmigrant status to B-2. This option is not available to J-1 nonimmigrants in a couple of cases, however:
If you are an international exchange visitor (J-1 nonimmigrant), you may not apply to change your nonimmigrant status if:
You were admitted to the United States to receive graduate medical training, unless you receive a special waiver, or
You are an exchange visitor and are required to meet the foreign residence requirement, unless you receive a waiver.
Switching nationalities won't help you at all, and might cause the authorities to doubt your intentions.