In this paper, we present a new connection provisioning algorithm for availability-aware optical transport networks planning regarding shareability of backup channels. The proposed scheme is designed to work under shared backup path protection policy and attempts to minimize the conflict between unavailability per connection and resource overbuild. It is adapted into a conventional two-step availability-constrained connection provisioning scheme. We evaluate the performance of this dynamic shareability driven connection provisioning scheme in terms of unavailability per connection and resource consumption as applied to NSFNET and EON topologies. Simulation results show that dynamic shareability driven connection provisioning scheme reduces the unavailability per connection by not violating the resource consumption as much as the dedicated path protection.