Coton training tips?

We have a 7 month old Coton, any tips for the following issues?

1.) when we take him for walks, he sometimes growls/barks at strangers on the street that are near us. He does this in the car when we are driving and might have pedestrians walking by our car. - I think he gets plenty of outdoor exposure, we take him for 5-6 walks per day and live in a city (there are usually people around). 3x a week he goes to a daycare and works with a trainer. On the weekends we take him to our in-laws, we sometimes take him to stores. The growling really only seems to happen on certain walks or in the car, not in these other instances.

2.) best tips for separation training? He seems to do fine when I leave him in his crate and go to lunch for 20 minutes. But we have tried leaving him with our in-laws and he gets pretty restless/barky. It really only seems to work if we tire him out, put him down for a nap, and then leave.