Here's the key to visiting Quebec:
"Bonjour! Je parle un petit peu de francais. Est-ce que tu parle anglais?"
In other words, don't go up to a French person and say "do you speak English?" Make an effort to ask them something in their language and they will be likely to respond in yours if they understand it.
We tried doing this in Montreal, and before we could finish the line we had one server laugh and say, "don't worry, we all speak English here."
In general though, yes, people appreciate it if you give it a shot. Sometimes they don't even mind if it's a similar Romance language.