I think some of these entirely depend on what the population of an area is made up of and the types of accents available. For example, for your second example, my area having a large centre of French speaking population, would speak it as spelled, even when English speakers are speaking the word. I've actually never heard the other pronunciation until I came across it while watching Outlander. Saint John would also be pronounced in full over here.
Speaking of native names, a fun one is Mackinac, such as in Mackinac Island in Michigan's UP. It's fun to hear people unfamiliar with it get tripped up. It's pronounced Ma-ki-naw. I recently saw a TV personality get tripped up by it on live TV.