but I think it is either modulating chords to modulate (i.e. change) from one key to another or, from your examples suggesting passing chords.
If it is the first case, modulating between keys, then Scaler supports this very well on the MOD page.
If it is the second case, passing chords, Scaler leaved this up to the composer.
In you first example you say
Can you clarify who or what has “suggested” this sequence, please? I know you use BIAB so is this where you get the “suggestion” from? If so it is only one of many possibilities, all of which may work.
I would suggest that because Cmaj and Amin are both within the key of Cmaj, and have two notes in common you do not need a passing chord unless you want a walking bass as in your example.; where the bass note walks down C->B->A.
There are other chords that will fit equally well as passing chords: C->F->Amin, C->Fmin->Amin (nice bit of anticipation here, I think), B->Bdim->Amin, C-Dmin/A,Amin, and so on. To my ear all of these work, but it is what sounds good to your ear that matters
The suggestion of C-Cmaj9-> A also sound good.
And all of these may be found using the Scaler Suggest option on the MAIN page or using the Progression option on the MOD page.