This is what I am thinking, I am thinking of either a Warhammer that weighs around 10lbs, and use it with the Versatile property, or a Maul.
The weapon may have Adamantium studs for the purpose of overcoming damage reduction.
The shield breaking property would be an opposed Athletics check, so for example my Athletics vs the opponent's Athletics.
If I will, the Kanabo minuses the shield's Armor Class by a permanent -1. Once the shield reaches 0 Armor Class, it is broken.
How does that sound?
P.S.
The reason the Kanabo has Adamantium studs is because each of my character's weapons will have a special property. He doesn't know it, but each one is "legendary" and gets more powerful as he gains proficiency bonus. Like for example, the Katana that shipped over that was his grandfather's is made of silver. Once he reaches proficiency level 3 (level 5), he will find out the Katana is also Magical (for the purpose of overcoming damage reduction).
Instead of getting new weapon, after new weapon, or replacement item, after replacement item, I figure it may be cool to have one that grows over time. Like the character learns more of the weapon's traits, and at the same time knows how to better use it.