Toronto is too far away for me right now (am up in Ottawa), but I lived in Toronto for about a year, up to last year, so know some about what you can do there.
Regarding the ROM, I have been there (on their annual free night), and I think they have a restaurant; most museums do. I didn't go there, though. I see this on the ROM's website, though:
link Apparently every Friday night they have a theme night (the first one looks to be this week). Next week they will have documentaries, for instance. I guess people who attend these can also explore the museum exhibits, too.
I would recommend the AGO over the ROM, in terms of collection, however, if you have been to other history and science museums, though. (There are many good things about the ROM, though, too, like their large rock collection; new galleries about Rome and the surrounding region that sound interesting, but were just being built when I was there; the mummies, which were more interesting than the ones at the Met in NY as they were more close-up; and one of the largest dinosaurs ever found (in Canada). Do take the tour of the ROM before you explore it yourself, as I found it quite informative (the tour guide told our group an interesting story about the dinosaur). On second thought after writing this, do check out the ROM, and also the AGO at some point.) Note that it is free to go to the AGO every Wednesday between 6pm and close (8:30pm). The ROM doesn't have a free night anymore, but reduced their ticket prices somewhat.
Yeah, I used to have a membership for the ROM, it was handy because we could go as many times as we wanted to and see all of the special exhibits. Is the AGO the art gallery of Ontario?