Luke 1:42 And she spake out with a loud voice, and said, Blessed [art] thou among women, and blessed [is] the fruit of thy womb.
(Of course, you have no scriptural support for even Gabriel praying to saints, do you?)
No, but I have scriptural support for Gabriel honoring Mary and saying to her "Hail, Full of Grace". And Mary is not dead. She's alive to God. We are still connected to the entire Body of Christ, past, present and future. Mary and the other saints can pray for us just as surely as you can pray for me.