Gosling's career doesn't need the help, though. If he wants a comic book franchise he can easily play Batman. No need to settle for being the Flash.
The Flash is a top hero. If a good actor (established or up-and-coming) can breathe life into the character with an amazing script and director then the film will be good.
Ledger never said that. He said he wasn't a fan of comic movies, not that he'd never act in one. 
Here's his quote
"I actually hate comic book movies, like f---ing hate them. They bore me and they're just dumb."
Gosling has stated numerous times he's not interested in doing comic movies, at the very least superhero movies.
Hmmm lol. If I hate something that's a pretty sure sign that I won't be involved with it lol. In this case I think if the right director and script is attached then an actor would be stupid to turn down a role that would help or benefit their career. Especially if the money is right.
I think Matt Bomer would compliment Cavill as Batman in a film. I can see a lot of other actors as Batman, but Matt has always been a favorite of mine also. Anson Mount would also make for a nice Batman.
I'm not opposed to Gosling as the Flash. The more I think about it the more it is starting to grow on me. As long as he could work well with an ensemble cast then I'm all for it. I would still rather see Timberlake or a similar actor in the role.
Duhamel is still my favorite choice for Hal Jordan. The guy looks dead like him and can act, has done drama, comedy, and action. Just look at him.
Sure he is on the taller side of 6'4, but that just means that his boots would be no more than an inch, where as Batman and Superman would wear at least 3-5 inch boots.
Casting for WW is hard. I've named 4-6 actresses I think would make a good WW. I haven't found that perfect 1, but the 4-6 I named can act, have presence and be able carry their own WW film or tv series.
The black guy from Fringe and Oz is starting to grow on me for J'onn/MM. I just want to see a tall, black actor with a commanding voice for the role
I wouldn't mind a slightly older Aquaman or someone around the same age as the other actors. I think Benedict Cumberbatch[sic] has an interesting look and would make a good Atlantean.
Think I'm going to start looking at blondes and redheads for WW and see if anyone might be a good choice lol.
p.s. The only choice I am 100% sure would make the best choice is my pic for hawkgirl lol. Dina Meyer from Starship Troopers looked, sounded, and acted just like Hawkgirl from JL/JLU. She's a bit on the older side (44), but i still think she would make the best Hawkgirl.