I had a similar situation at CDG several years ago, albeit a bigger aircraft and I was in J. I only had carryon. This package (also breakable) was in actuality a third piece. I went to checkin although I already had done online. Was honest about the situation. I was exceedingly lucky that the AC rep was just superb. Couldn’t ask for better. He personally wrapped it in a more protective covering (store had bubble on it) and put a couple of stickers on it so I wouldn’t have issues at security. Explained to SD onboard and she found a safe place for it. Staring at the item (in my home) as I write and feeling grateful to AC for helping me out.

Fyi, also saw something similar on Air NZ many years ago. Couple beside me brought a painting on board. Treated in a similar way to what I describe above. Have no idea if they made a special arrangement in advance.

My fingers are crossed for you.