Am I entitled to US Visa Waiver Program?

As Mark Mayo notes, VWP eligibility is determined based on the citizenship under which you are applying, regardless of how long you have held that citizenship or what other citizenships you may hold, or may have held in the past.

There are some circumstances under which you would not be eligible for the visa waiver program, however. Specifically, you are not eligible if any of the following conditions is true:

• You have been found ineligible for a US visa (regardless of the passport you used when applying for the visa) [note that this requirement appears not to be absolute; Gervasio Marchand mentions in a comment that he received ESTA approval despite disclosing a past visa denial. My point here, however, is that using your Scandinavian passport does not "erase" any adverse immigration history you may have accrued using your Pakistani passport]
• You have been admitted to the US in the past, but failed to comply with the conditions of your admission
• You have a passport that does not meet the requirements (generally, it must have an integrated chip, but there are exceptions; see the linked page for details)
• You are traveling on a private aircraft or on a carrier who is not approved for the VWP
• You intend to stay longer than 90 days or you intend to change your immigration status after you arrive
• You are traveling to the US for a purpose other than those approved for the VWP (these are generally B1/B2 purposes -- business visitor or tourist; see the page linked below for details)

The above information is taken from http://travel.state.gov/content/visas/en/visit/visa-waiver-program.html.

If you have been issued a US visa in your Pakistani passport, it is unclear whether you can nonetheless travel on the VWP using your Scandinavian passport. The frequently asked questions for ESTA do not address this question specifically.

If you have an unexpired US visa in your Pakistani passport, you can save yourself $14 by using it to travel, unless, of course, you are no longer a Pakistani citizen. In that case, you might want to ask at the nearest US consulate whether you need to have the visa revoked.

I would be interested to know whether you are in fact accepted when you apply for your ESTA, as I imagine many others on this site would be. I do not know whether the information requested in the application would allow them to identify you as a Pakistani by birth, or as a recently-naturalized citizen of your new country.

If your ESTA application is denied, you will have to apply for a visa. Therefore, you should apply for ESTA well in advance of your intended travel date, so there is sufficient time for a visa application in case it is necessary.