[Richard Jeong]

Is borate ester a good leaving group as halogen?

if yes, I want to know whether metalation is possible or not.

[rolnor]

Have you seen metalation with any ester, even good leavingroups like mesylate or triflate?  Maby you mean reductive elimination with palladium(0) then boronic acids are used.

[Babcock_Hall]

As a rough first approximation, I would look at the pK_a values of the conjugate acids of the leaving groups.