But when? As I read the Singapore rules there is no exception: those vaccinated in the US or Canada must have a SMART card. And yes, it will be impossible for many people to obtain one.
Even if your state or province isn’t vaccine passport friendly, pharmacies in those states and provinces are providing QR codes. CVS in Florida and Georgia, for example, are providing QR codes. And CVS is on the CommonPass network regardless of state government objections. Check with the provider you received your vaccination from.
I uploaded my CVS QR to CommonPass last night and had no problems getting a CommonPass QR. My vaccine was administered in the bright red south.