The answers to a few quick questions may help clarify what places might meet your needs...
1. Since you want to avoid downtown, perhaps you can indicate what general area (which city neighborhoods or suburban towns) would be your ideal location?
2. Did you only look on Opentable to see what's available, or did you also look at
their listings of specific Dec 24 plans by their restaurants?
3. Do you prefer a place that does a special brunch meal for the holiday? Or would you consider a restaurant that normally serves a really good lunch, even if it isn't brunch-ish (i.e. no breakfast-type dishes) and may not be doing anything special for the holiday? (Looking at the availability on Opentable, I see quite a few restaurants that are perfectly fine for a nice weekday lunch, but I'm not sure whether that's what you're looking for.)
4. I know you said you would
prefer to make a reservation, but if your objective is to be able to choose from both breakfast and lunch items, would you consider one of our breakfast-focused restaurants that don't accept them (e.g. Jam, M. Henry, M. Henrietta, Bongo Room, Southport Grocery, Walker Brothers, Marmalade)? I know those places get slammed on weekends, but I have absolutely no idea how busy they might be on Dec 24, which is a Monday.