No. Zero chance.
Previous WestJet leadership dismissed the idea of joining any alliance — repeatedly and adamantly. They said they’d only ever do one-on-one relationships (ie code-sharing).
Now, new WestJet leadership wants to transition the airline to being a regionally-focused leisure carrier for vacationers. Not only is that not a fit for SkyTeam (or any alliance), I think that may even put their current level of partnership with Delta at risk.
SkyTeam? Not going to happen.