Talk to Wild Ginger. They won't have the typical Chinese wedding menu (long life noodles or whatever), but they can put together a family style dinner with a respectable menu. I believe at their Seattle location you can do 100, but can't recall if they do so by opening up the walls between rooms or if you are broken up into multiple rooms.
You didn't specify what kind of Asian food you were looking, but you might take a look at the O'Asian website.
Looks like they have a private room that can accomodate 100. There's a sample menu - I wasn't able to view it online, but I was able to view it after I saved it to my desktop rather than trying to open it directly.
Both are in Renton. Neither are very good with top end food in my opinion, and will be fairly disappointing especially if there are guests coming from Asia. But they do have the proper facilities for 100 people.
I'm not sure if high standards are required for the food (I have no idea where you're from) - but if the wedding party is trying to conform to the wishes of traditional Asian parents by putting a traditional wedding banquet together, bringing said parents to a food tasting would nix that idea pretty quickly. Although considering the state of wedding food in general, maybe it's not that big of a deal in the end, and it's the thought that counts. You could do worse - like eating rubber chicken at the top of the Space Needle, for instance.
I have been to at least 10-15 weddings with Chinese couples in recent memory and only one of them opted to do a traditional Chinese banquet. It was a horrifying experience.
Tea Palace Restaurant
2828 Sunset, Renton, WA 98055
I think that the New Hong Kong Seafood (formerly New Kowloon) would be able to provide a space big enough. Cannot think of many others off the top of my head. They have the additonal positive feature of having parking in the building.
New Hong Kong Restaurant
900 S Jackson St Ste 201, Seattle, WA 98104