I'm not sure it deserves a response but I'll bite.
Giroud scored 33 L1 goals in 73 games, playing lone striker and shooting penalties.
Cavani has scored 44 L1 goals in 81 games, playing LW and not shooting penalties.
Overall in their careers, Giroud has scored 132 goals in 308 games, including many L2 (and National) games.
Cavani has scored 165 goals in 318 games, playing top flight football, facing tougher defenses and playing wing for the last 81 games.
For Arsenal? Cavani wouldn't be an upgrade with his poor finishing. In the top flight, Giroud has 115 goals in 249 games with Arsenal/Montpellier. We've seen him score goals against all of the big clubs, and we've seen him get better since he joined Arsenal. He's strong in the air, makes good runs, is good all around, and is a perfect fit for Arsenal. If you want to critique him, I suppose his finishing up to par, but if it were, he'd be setting records in the EPL. If you're going to look for an upgrade, you want somebody who can finish, and Cavani can't finish.
You already know how I feel about Cavani. Take away his absurd totals in Napoli, and Cavani's top flight totals? 106 in 237 games. Built up by destroying crap teams, as I've evidenced in the past.
Giroud gets an absurd amount of hate because he plays for Arsenal, and everybody hates Arsenal. RVP had a slightly higher GPG than Giroud. A single percent higher.
Next month, in the CL, I would put my life down betting that Giroud has a better performance than Cavani. Even with Giroud going against Barca getting zero chances, and Cavani having to play against Chelsea.
Cavani as a winger, I would totally be ok with, and he'd obviously be better than Giroud. But as a striker? It's not even a question.