For months, the 2020 iPad Pro release had been a given for March.
Really, are you sure about that? An iPhone SE 2 event was scheduled for March and that indeed has been cancelled. But there wouldn't be any near ready iPad 2020 product to show this month (March). It would have been a very difficult exercise to launch a product that doesn't exist yet! The A14X chips to be used in the 2020 iPad will start rolling off TSMC's production lines some time in April, probably. Perhaps, there will be something to show at WWDC in June but it is improbable that products will make it to market before September or October.
The iPhone SE 2, if Apple still wants to launch it, might be ready by June but I don't think we will see the 2020 iPhone until September or thereabouts.