Archer > Cannon > Falconer > Hunter
This build is for fighting large groups of monsters, like challenge mode or hunting grounds.
Cannon deals most damage.
Falconer deals extra AoE damage with Tomahawk, Pheasant, Sonic Strike. Roost resets cooldowns even more. Circling helps a lot because it reduces AoE defense to 1, allowing you to damage more monsters while in Bazooka stance.
Hunter is your mob-control class. Growling holds and prevents monsters from attacking. Hounding increases loot chance by +500.
If you do not want to use companions, I suggest this build:
Archer > Cannon > Pied Piper > Sapper
Cannon deals most of your damage.
Piper lets you control mobs, position them so you can blast them away with your AoE skills. Lied Des Weltbaum will double the damage you deal and take. Use this first, then control mobs with Dissonanz, Wiegenlied, or Hypnotische Floete so you can unload with damage. *I skipped Hameln Nagetir because the damage is crap
Sapper adds more AoE damage plus a little extra mob control. Use Broom Trap against huge mobs, damaging and slowing them. Organize smaller clumps of loose mobs into a ball with Hynotische Floete then slap with Punji Stake. Stake Stockades adds a little extra damage, while the other traps help hold/push mobs away. *Skip Claymore because the damage and AoE is not worth it.
I used to main Cannoneer before the changes to Bazooka, and I was able to do a fair bit of damage back then. Lvl15 Cannon Shot + Bazooka used to deal 4,090% damage on ground targets–maybe 6,136% with Smoke Grenade. Shootdown also used to help with flying monsters, adding bonus damage to flyers.
Huge nerfs came though.
Now we only have Cannon Shot that deals 946% on ground targets, 400% on air targets with Bazooka and Smoke Grenade no longer adding bonus damage to Cannon skills. Factor in the limited 6 AoE, and you will have trouble dealing with large groups of mobs like in challenge mode or hunting grounds.
Long story short: skip cannoneer and get a wizard or scout for farming.