THe museum that would want it would be wherever she was married. If it was in Toronto then you should approach the Toronto Historical Board, not the ROM. The ROM doesn't collect local items, in fact I think they try hard not to!
The TOronto Historical Board operates all the various historic sites in Toronto - Spadina House, MacKenzie house, Todmorden Mills, COlborne Lodge, Montgomery's Inn, etc. and they have a huge storage facility in Parkdale. There have been plans for a while to build a museum of TOronto somewhere on the waterfront and it will become more likely in the years to come, so if you prefer it to go to a museum, I would suggest you approach them. If she was married somewhere else, then contact the town where she was married.
For resale, I think you are going to find that condition is key. It will have to be displayable, and if the silk has begun to shatter then it won't sell well. If it is sturdy and you have all the history, including a copy of the photograph to include with the sale, then it will probably go to a collector, and because its also a peg top or hobble dress (words I would try to squeeze into the title or description) it has some added interest.
I agree with Hollis, check out similar wedding dresses on eBay to see their final prices, and any time of year to sell it is fine.
Also, Casa Loma collects clothing of the period when Lord and Lady Pellett owned the house (1911 - 1922) and Seneca Fashion Resource Centre might be into collecting it as an example of a peg top dress from 1913... Hell, I will take it for the Fashion History Museum in Cambridge, except we are in the middle of getting our charitable status so I can't offer a tax receipt until next year.
