It depends, but Toucannon has a bit of a shallow movepool for in game purposes without Bullet Seed and Rock Blast.
The moves I see working best for Toucannon in game not including multi hit moves would be Drill Peck, U-turn, Brick Break, Return (if it has high friendship)/Frustration (if it has low friendship), and, if you're willing to earn some BP (if this is in USUM), Seed Bomb.
As you can see, that's not a lot of options. So, I would use Rock Blast, but if this is USUM, go with Seed Bomb over Bullet Seed. I would try Drill Peck, Rock Blast, Seed Bomb/Bullet Seed, and U-turn, personally.
Hope this helps! :)