Converting from an LLC to a C Corp; can we use the same EIN?

No. You'll likely need a new EIN. Per the IRS website:

Generally, businesses need a new EIN when their ownership or structure has changed.

Also,

Partnerships

You will be required to obtain a new EIN if any of the following statements are true.

• You incorporate.

The following EIN document created by the IRS may also be helpful: Understanding Your EIN

Someone is likely to point out that the OP has an LLC, not a partnership. Please note the following from the same website:

Limited Liability Company (LLC)

An LLC is an entity created by state statute. The IRS did not create a new tax classification for the LLC when it was created by the states; instead IRS uses the tax entity classifications it has always had for business taxpayers: corporation, partnership, or disregarded as an entity separate from its owner, referred to as a “disregarded entity.” An LLC is always classified by the IRS as one of these types of taxable entities.