OneWorld makes no sense. Skyteam is the only option and realistically should happen sooner rather than later as Westjet needs those partner relationships in order to fill their 787. They need the AirFrance and KLM and maybe even Alitalia connections out of CDG and LGW.
The relationship with Delta is already in place so the only logical choice is Skyteam. I think management will quickly see the importance and value of membership in order to attract customers and will make it happen in 2020.