Velvet Goldmine
Having played the original Raoul and the second Phantom on Broadway, I’d say he could. Until he commited suicide.
I checked their Bios and it turns out that they are both from Melbourne.
Craig Ferguson sounds Scottish to me but he’s mentioned on his show that on trips back home family and friends comment/complain that he speaks in an American accent.
Anthony LaPaglia’s accent might be a conscious effort. Dominic Purcell (I think) mentioned in an interview when he started acting in the US, LaPaglia told him if he wanted to get the accent right he should speak like an American even when out of character.
Courteney Cox was raised in Alabama and apparently had a strong Southern accent until she went into acting and had it trained out of her. You don’t hear any accent now.
I haven’t pinned it down. They can both be rather grating. Not as bad as a white South African accent, which makes me feel stabby.
Ask them to say H, other than that I haven’t a clue how you would tell a Catholic from a Protestant by their accent. 
Err, I went to high school with Gillian and her younger brother went to the same school while my younger brother was there - neither of them had any trace of an accent other than “Michigan.”
I’m not sure what your point is. Anderson returned to the United States when she was eleven (an age at which most children would be in fifth or sixth grade). She then learned to speak with an American accent. When you went to high school with her, she had an American accent.
My colleague has heard of this and it sounds to me like Protestants pronounce H like the Scottish do and the Catholics pronounce H like the English.
Scottish/Protestant = 'aitch
English/Catholic - Haitch
Pronouncing single letters rarely comes up in conversation though.
You’d be better of asking someone what school they went to. 
Daniel Davis, best known as Niles the Butler on the Nanny, is an Arkansas native who can speak with a broad Southern accent.
I read a magazine interview with Pierce Brosnan in which he lamented no longer being able to speak in his original Irish accent. He said it had been “beaten out of” him at school because his English classmates kept wanting to fight him when they heard him speak.
Anthony Head, too, right?
I’ve heard Anthony Head speak in his non-R.P. accent in interviews. Almost all British actors are trained in a stage accent, so there’s not much point in listing all of them.
I could be wrong but I thought Haitch wasn’t common in England either. Anyway my point was I don’t think it actually is possible.
I can only imagine what Ava Gardner might have sounded like before she had that rural NC accent homogenized out of her. I’ll go out on a limb and say that it probably was a little different from what you heard onscreen. Ava Gardner. . . [sigh]
One of Higgins’ (Hillerman’s *Magnum *character) many half brothers was a Texan.
Kathleen Turner was born in Missouri, but her father was in the Diplomatic Service, and she spent a significant part of her formative years in Venezuela. In interviews, she speaks with a strong accent, but acts with a Midwestern white-bread speaking style.
I don’t think it’s so much that she “Had” to learn an accent - it’s not a law - as she would have just naturally adopted an American accent.
People’s accent do change, even as adults. Portia de Rossi, to use the example in the OP, has lived in California for almost half her life. It wouldn’t be at all unusual for her accent to simply have changed.
I think it’s rather easy to hear Julia Roberts’s Southernness in her voice. I picked her out as a Southerner from the get-go.
As Buffy fans know, you can hear a reasonable approximation of Head’s original accent in the on-screen speech of (American) actor James Marsters, who played Spike.
Really? Believe me, her accent is nothing compared to those of her classmates at Campbell High.