Is the sunlight on the GOES-16 Imagery reaching from the east?
Yes. The time stamp says that the image is taken at 13:45Z, which means the sun is overhead in the Eastern Atlantic (12:45 PM local time in Cabo Verde and the Azores). In Winnepeg, near the upper arrow, it is 7:45 AM and still in darkness.

Being winter in the NH, places that are more southerly like Louisiana and east Texas in the US have light while places at the same longitude further north do not.

You can tell that the image is taken in winter from the south-west to north-east slope of the terminator (i.e. the line separating the light and dark areas, see discussion here).