<PAGE>

                                                                   EXHIBIT 10.20

                                 April 20, 2004

Board of Directors
Omega Financial Corporation
366 Walker Drive
State College, PA 16804

            RE:   Shareholder Voting Agreement (this "Agreement")

Dear Ladies and Gentlemen:

      The undersigned Shareholder ("SHAREHOLDER") of Sun Bancorp, Inc., a
Pennsylvania corporation ("SUN"), in order to induce Omega Financial
Corporation, a Pennsylvania corporation ("OMEGA") to enter into the Agreement
and Plan of Merger, of even date, by and between Omega and Sun (the "MERGER
AGREEMENT") hereby represents, warrants and agrees as follows:

      1.    Shareholder hereby represents and warrants that Shareholder owns of
record and beneficially (as defined in Rule 13d-3 under the Exchange Act), good
and valid title to all of the shares of the capital stock of Sun, and options to
acquire shares of capital stock of Sun, shown on Exhibit A attached hereto, free
and clear of any and all mortgages, liens, encumbrances, charges, claims,
restrictions, pledges, security interests, voting trusts or agreements, or
impositions, except as otherwise disclosed on Exhibit A, and such shares
represent all of the shares, or rights to acquire shares, of capital stock of
Sun owned by Shareholder. For purposes hereof, the shares of capital stock of
Sun and the options to acquire shares of capital stock of Sun set forth on
Exhibit A attached hereto, and any such shares and options hereafter acquired by
Shareholder, shall be referred to herein as the "Stock." It is understood and
agreed that the term "Stock" shall not include any securities owned by
Shareholder as a trustee or fiduciary of a trust or account of which they are
not the principal beneficiary, and that this Agreement is not in any way
intended to affect the exercise by the Shareholder of Shareholder's fiduciary
responsibility with respect to any such securities.

      2.    Shareholder will vote, or cause to be voted, all of the Stock in
person or by proxy, (a) for approval of the Merger Agreement and the
transactions contemplated thereby at any meeting of the Sun shareholders duly
held for such purpose, and (b) against any action or proposal that is intended,
or could reasonably be expected, to impede, interfere with, delay, or adversely
affect the transactions contemplated by the Merger Agreement. In the event that
any vote of any of the Stock does not comply with the terms of this Agreement,
such vote shall be considered null and void, and the provisions of Section 3 of
this Agreement shall immediately take effect.

<PAGE>

      3.    Shareholder hereby irrevocably constitutes and appoints Omega, or
its designee, from and after the date hereof and until the termination of this
Agreement as provided herein (at which point such constitution and appointment
shall automatically be revoked) as Shareholder's attorney, agent and proxy (such
constitution and appointment, the "Irrevocable Proxy"), with full power of
substitution, to vote and otherwise act with respect to all such Shareholder's
Shares at any meeting of the shareholders of Sun (whether annual or special and
whether or not an adjourned or postponed meeting), however called, and in any
action by written consent of the shareholders of Sun, on the matters and in the
manner specified in Section 2 above. Without limiting the foregoing, in any such
vote or other action pursuant to such proxy, neither Omega nor any other person
listed in the immediately preceding sentence shall in any event have the right
(and such proxy shall not confer the right) to vote against the Merger. THIS
PROXY AND POWER OF ATTORNEY ARE IRREVOCABLE (UNTIL TERMINATED AS PROVIDED
HEREIN) AND COUPLED WITH AN INTEREST AND, TO THE EXTENT PERMITTED UNDER
APPLICABLE LAW, SHALL BE VALID AND BINDING ON ANY PERSON TO WHOM A SHAREHOLDER
MAY TRANSFER ANY OF ITS SHARES IN BREACH OF THIS AGREEMENT. Shareholder hereby
revokes all other proxies and powers of attorney with respect to all
Shareholder's Shares that may have heretofore been appointed or granted, and no
subsequent proxy or power of attorney shall be given (and if given, shall not be
effective) by Shareholder with respect thereto. All authority herein conferred
or agreed to be conferred shall survive the death or incapacity of Shareholder
and any obligation of Shareholder under this Agreement shall be binding upon the
heirs, personal representatives, successors and assigns of Shareholder.

      4.    Shareholder will not, nor will Shareholder permit any Person under
Shareholder's "control" (as defined for purposes of Rule 144 under the
Securities Act) to, deposit any of the Stock in a voting trust or subject any of
the Stock to any arrangement with respect to the voting of the Stock in any
manner inconsistent with this Agreement.

      5.    Shareholder will not sell, transfer, pledge, give, hypothecate,
assign or otherwise alienate or transfer, by proxy or otherwise (including any
transfer by operation of law), the Stock or any of Shareholder's voting rights
with respect to the Stock, except as otherwise disclosed on Exhibit A.

      6.    Irreparable damage would occur in the event any of the provisions of
this Agreement were not performed in accordance with the terms hereof and,
therefore, Omega shall be entitled to specific performance of the terms hereof,
in addition to any other remedy at law or equity to which it may be entitled.

      7.    The execution and delivery of this Agreement by Shareholder does
not, and the performance by Shareholder of its obligations hereunder will not,
constitute a violation of, conflict with, result in a default (or an event
which, with notice or lapse of time or both, would result in a default) under,
or result in the creation of any lien on any of such Stock under, (i) any
contract, commitment or agreement, to which Shareholder is a party or by which
Shareholder is bound, (ii) any Applicable Law, or (iii) the organizational
documents of Shareholder, if applicable.

<PAGE>

      8.    Shareholder has full power and authority to execute, deliver and
perform this Agreement, to vote the Stock as required herein and to consummate
the transactions contemplated hereby. The execution, delivery and performance of
this Agreement and the consummation of the transactions contemplated hereby have
been duly and validly authorized and no other actions on the part of Shareholder
are required in order to consummate the transaction contemplated hereby. This
Agreement has been duly and validly executed and delivered by Shareholder and
constitutes a valid and binding agreement of Shareholder, enforceable against
Shareholder in accordance with its terms.

      9.    This Agreement constitutes the entire agreement between the parties
with respect to the subject matter hereof and supersedes all other prior
agreements and understandings, both written and oral, between the parties with
respect to the subject matter hereof, and shall be binding upon the successors
and assigns (as applicable) of the parties hereto.

      10.   This Agreement will be governed by and construed in accordance with
the laws of the Commonwealth of Pennsylvania regardless of the laws that might
otherwise govern under applicable principles of conflicts of laws thereof.

      11.   Any term or provision of this Agreement that is held by a court of
competent jurisdiction or other authority to be invalid, void or unenforceable
in any situation in any jurisdiction shall not affect the validity or
enforceability of the remaining terms and provisions hereof or the validity or
enforceability of the offending term or provision in any other situation or in
any other jurisdiction.

      12.   No failure on the part of either party hereto to exercise any power,
right, privilege or remedy under this Agreement, and no delay on the part of
either party in exercising any power, right, privilege or remedy under this
Agreement, shall operate as a waiver of such power, right, privilege or remedy;
and no single or partial exercise of any such power, right, privilege or remedy
shall preclude any other or further exercise thereof or of any other power,
right, privilege or remedy. Neither party shall be deemed to have waived any
claim arising out of this Agreement, or any power, right, privilege or remedy
under this Agreement, unless the waiver of such claim, power, right, privilege
or remedy is expressly set forth in a written instrument duly executed and
delivered on behalf of such party; and any such waiver shall not be applicable
or have any effect except in the specific instance in which it is given. This
Agreement may not be amended except by an instrument in writing signed by
Shareholder and Omega.

      13.   Capitalized terms not otherwise defined herein shall have the
meanings given to them in the Merger Agreement. Shareholder and Omega shall be
deemed to be the sole "parties" to this Agreement.

      14.   Shareholder understands and acknowledges that Omega is entering into
the Merger Agreement in reliance upon Shareholder's execution, delivery and
performance of this Agreement.

      15.   It is understood and hereby agreed that this Agreement relates
solely to the capacity of Shareholder as a shareholder of Sun and owner of the
Stock and is not in any way

<PAGE>

intended to affect the exercise of Shareholder's responsibilities and fiduciary
duties as a director or officer of Sun or any of its Subsidiaries, which
responsibilities and fiduciary duties take precedence over Shareholder's
position as a Sun Shareholder. Notwithstanding the foregoing, Shareholder
acknowledges and agrees that the exercise of Shareholder's responsibilities and
fiduciary duties as a director or officer of Sun shall not, in any respect,
affect or alter, or be deemed to permit Shareholder to terminate or circumvent,
Shareholder's obligation to comply with the terms of this Agreement (including,
without limitation, Shareholder's obligations under Section 2 hereof), nor, with
respect to the Stock, shall the exercise of any such responsibilities and
fiduciary duties by Shareholder affect any of Omega's rights hereunder.

      16.   This Agreement shall terminate on the earliest of (a) the date that
the Merger Agreement is terminated in accordance with its terms, (b) the
Effective Time or (c) December 31, 2004.

                                            Very truly yours,

                                             /s/ Sidney M. Palmer
                                            -------------------------------
                                            Printed Name: Sidney M. Palmer

ACKNOWLEDGED AND AGREED:

OMEGA FINANCIAL CORPORATION

By:    David Lee
    ----------------------------------
     Name:  David Lee
     Title: Chairman and Chief Executive
            Officer