Baumi
Adventurer
My group had a small Rules Discussion and we thought to ask the collective Wisdom of ENWorld. 
When can you substitute an Attack for a Shove or Grapple?
It's clear that you can change your normal Attacks (even part of Multi-Attack) to them, but what about Bonus Action Attacks like the ones from the Polearm Master Feat or Two-Weapon Fighting? Also can you change your Opportunity Attacks (which would make you far more sticky then just dealing damage)?

When can you substitute an Attack for a Shove or Grapple?
It's clear that you can change your normal Attacks (even part of Multi-Attack) to them, but what about Bonus Action Attacks like the ones from the Polearm Master Feat or Two-Weapon Fighting? Also can you change your Opportunity Attacks (which would make you far more sticky then just dealing damage)?