I have no proof, but a good possibility for the parents of your John Stowe Wainwright would be Joseph Wainwright & Martha Stowe. Paternal grandparents would be Benjamin Wainwright & Keturah Stowe, maternal grandparents would be John Stowe & Jane Joell.
I think this is a possibility because all of this John Wainwright's brothers had "Stowe" as middle names.
Joseph WAINWRIGHT ( - 1811/1812) & Martha STOWE (1773 - ) children: John WAINWRIGHT Benjamin WAINWRIGHT (1797 - ) Joseph Stowe WAINWRIGHT (1800 - ) Solomon Joell Stowe WAINWRIGHT (1801 - ) William Graham Stowe WAINWRIGHT (1804 - ) Keturah Jane WAINWRIGHT (1806 - ) m. Thomas STOWE ( - Before 1826) Mary Esther WAINWRIGHT (1809 - Nov 1811)
Will of Joseph Wainwright of Pembroke dated 12 Jan 1811, proved 11 Feb 1814 Wife Martha (Stowe), ch: John, Benjamin, Solomon, William, Keturah, Mary exec: none named wit: William Joell, William Stowe admin of estate on 9 Jun 1814 to Mrs Martha Wainwright, John & Joseph Stowe
This information comes from my research of the Bermuda Joell line.