How many people would respond to me in French vs English in Sherbrooke?

Sorry for the English. I want to learn French and I'm from the US and thinking about moving to the Quebec-US border.

If I went to Sherbrooke during the weekend how many people would respond in French once I got to a conversational level? What about when I were fluent? Once I'm not a nuisance to talk to in French due to my level I don't want to be responded to in English. Is there a better city or town than Sherbrooke for me that is a within 2-3 hours of driving from the US (the closer the better)?