Canadian PR with a valid US visa: Is a US layover still low-risk for Caribbean travel?

Please, let's not be political. We all have opinions, but I'm just trying to get practical, helpful advice from people familiar with US immigration procedures.

Background: I am South American with a South American passport. I am a permanent resident of Canada, and I have a valid US tourism visa. I've successfully travelled to the US several times for tourism in the past 7 years. I have no criminal record or legal issues, not even a speeding ticket, in either country.

Recently, I haven't travelled to the US and I haven't done any travelling that would have a layover through the US, and I'm considering a Caribbean vacation where the only reasonable flight options involve a US layover.

My questions are:
A. What is the practical risk for me to travel to the Caribbean with a layover in the US? Meaning, is there any chance I could be randomly detained even without any obvious reasons?

B. When travelling out of Canada, for some airports, US customs is done while in Canada. Is the same true for certain Caribbean countries when returning to Canada through the US? And if so, which countries? For example, if I go to the Bahamas, I'll go through US customs checks while still in Canada, then go to the US, get off the plane, board the other plane, go to Bahamas. Then on the way back, will I go through US customs while still on the Bahamas, or in the US?

I'm asking this last question because I think (but I could be wrong) that being in another country reduces the chance of being randomly detained.

PS - I know airport security screening is done in the US regardless
PPS - From where I'm departing, no direct flights to some Caribbean countries exist - all flights seem to go through the US.