Murrow grew up in Washington state near the Canadian border after age 6 or so. Then again, he came into broadcasting in an era (1930s) when standard radio speech was more Northeast than Midwest, and he had the appropriate round-voweled, slightly stuffy, diction-conscious delivery.
For a Southerner whose accent only mellowed over time, cue up David Brinkley (Wilmington, NC).
I regret to inform you that people from Toronto do indeed have a distinct accent. We call them Toronto Valley Girls. 
And all you U.S. Americans sound funny to me. My husband says my accent is that I pronounce things clearly, the same as my mother.
I think one of the most persistent accents is a British one. I knew a guy who was born in raised in Canada by British parents, and even he had a British accent.
What do Torontonians sound like?
The mean answer is that they mention “Toronto” in every sentence.
More serious answer; for starters, they’re the ones giving Canadians a reputation for saying “oot” and “aboot.” Well, them and Newfies. It’s hard to exactly describe a Toronto accent, but I know it when I hear it. It’s like the Alberta accent; I can’t really describe that, either, but I know it when I hear it. Fortunately us people from Saskatchewan have no discernible accent.
I’ve spent a fair bit of time in Canada and never heard anyone say “oot / aboot.”
What they DO say, in varying degrees, is somewhere between “oat / aboat” and “ehwt / abehwt.” And strangely enough, it’s much less pronounced in any other word with the ow sound in it.
Even stranger is that Canadians whose speech has been Americanized in every other way will still pronounce those two words differently, as a sort of semi-conscious signifier of national identity.
I am one who believes that the generic supposedly Midwestern speech pattern is caused by an averaging effect rather than being a naturally occurring accent that tended to get picked up by lots of Americans. One of my pieces of evidence would be visiting any national university (one that is prestigious enough to pull students from nearly all states). Well within the first year, the students from New Jersey as well as those from Appalachia and almost everywhere else will follow roughly the same speech pattern unintentionally. I grew up in Northern Louisiana with a very strong Southern accent. I went to a national university and my accent faded quickly basically against my will. I then went to an Ivy League university for grad school (Dartmouth) in New England and later moved to Boston. As of three years ago some people could detect a trace of Southern accent but it hasn’t happened for a long while so I assume it is all but gone now.
The alternative to the averaging effect for a standard U.S, accent is that someone would pick up bits and pieces of new accents as they move around. That may happen as a small effect but not as a large one. In my case, I would have a speech pattern that combines strong Southern, New Orleans speech, New Hampshire/Vermont as well as Boston. Insert not just the pukey smiley here but also the projectile vomiting one. Luckily, that didn’t happen to me just like it doesn’t to nearly anyone that moves around to areas with various distinctive accents. Accents to to converge rather than simply integrate into one another.
You would be diphthonging yourself into early grave, you would.
Here’s a hypothesis I want to test on y’all/youins/youse. I live in the greater NYC metroplex and happen to hear a lot of educated people speak on TV, radio and the like. My hypothesis - I’d call it a theory, except I haven’t been keeping hard data - is that New York ethnic accents survive higher education and white-collar professions more strongly than any others.
My explanation is that intellectual and professional achievement are, in a way, the cultural currency of the region. Shelby Foote could talk like a Mississippian because the South was his area of study, but imagine if he’d become a theoretical physicist. A New Yorker can talk like a New Yorker even if his field covers the globe.
Flip!
Any other regional US accents, that is.
I said my accent is “generic and placeless,” i.e., people do not know where I am from based on the way I talk. The same way that newscasters have a generic “placeless” accent that most people would call “no accent.”
However, the next time somebody tells me that I don’t have an accent, I will hasten to correct them just as you did.
Another data point: I grew up in the deep south and can easily distinguish many sub-accents among the general southern accent. I can pick out regions in GA I can tell NC, from TN from AL, from Miss. I went to two national universities and lived outside the south (upper midwest) for many years. (I can tell MN from WI)
My accent, though, only changed once–when I got to college a little bit of my rural twang left me–but not much. Since then, despite my fairly wide exposure and my great interest in the subject, my accent has remained very southern.