I'd say you're on the right track. But maybe you're thinking too much about it. 24" x 25" is a big enlargement, but both the 7D and film can handle it. Personally, I'd stick with the 7D as you can check the file on your monitor before getting it printed. With work, I regularly print A1 sized posters from similar cameras. That's 23.39 Ã— 33.11. Admittedly, if you look very very closely, you can identify some pixelation. Film at this level of enlargement also shows grain and is a bit harder to print. My Personal opinion - at such a high enlargement, I can almost guarantee you'll get a sharper, crisper print in digital than 35mm film. Unless you've got a very sharp photo, and using a good lab, 35mm film tends to look a bit soft after 11x14. In fact, I've got a big medium format enlarger, and it won't even enlarge 35mm beyond 11x14, but a professional lab shouldn't have any problems going bigger. Of course, if they are scanning the file first, which is more common these days, then that adds another step for the image to be degraded. End of the day, I'd stick to digital.
But for all intensive purposes, both should look fine. Once you have yours inside a frame, 24x25 should look fantastic. I'd be more focused on getting a good photo - eg expression, smile, pleasing background etc. Try some with the tripod, as any camera shake will be magnified. But if you like the photo, and it looks good enlarged on your monitor, it should print fine.
If you're indoors (or even outdoors) have you considered a flash (or two)? Bounced off a wall or ceiling, it can help produce good effects and help keep a high shutter speed (reducing the possibility of camera shake).