Yep! All you have to do is send out Magearna and Smeargle in a double battle (in-game, and not in the Battle Tree). Make sure that Magearna is faster than Smeargle so that Sketch is used after Fleur Cannon. Et voila! Fleur Cannon Smeargle!
… of course, finding a double battle in-game can be tough, because there are no rematches and you've probably fought them already. In that case, there is still a way to get Fleur Cannon Smeargle, but it takes longer.
First, you have to find a Smeargle in the wild. Use False Swipe, which the Smeargle will then Sketch, and an Adrenaline Orb. Switch to Magearna. Wait until Smeargle calls an ally, then KO the first Smeargle with Fleur Cannon. The ally Smeargle will then use Sketch and learn Fleur Cannon. Switch out Magearna and False Swipe/Paralyze the Smeargle (paralysis stops it from calling for help.) Once it has stopped calling allies, catch it. Et voila! Fleur Cannon Smeargle!