Hello Julz!
To answer your questions, if you truly wanted to you could "seal" your whole face. However, you would need a couple of products to do so.
Face
If you wanted to seal your foundation, you should use one of the following products:
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Cinema Secrets Super Sealer Spray. It costs $6.95, and it is sold at a store out here in Burbank, CA called Cinema Secrets. It's a store specifically designed to serve makeup and special effects artists in the TV, Film and commerical industry. We use it to set actors makeup in Tv, film, commerical photo shoots, runway, etc. but I find I also like to use it on my brides to help thier makeup stay on through the ceremony and reception. To order it, you can call (818)846-0579.
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Model In a Bottle is a "commercialized" version of the Super Sealer Spray, and therefore it is more expensive. For the original formula, it will cost you $18 and for the Sensitive Skin Formulation it will be $21. You can find this product at
www.modelinabottle.com and some salons actually carry it in stock, so you can call your local salons and ask them if they have it in stock.
Eyes, Brows and Lips
To seal the rest of your makeup, I would highly suggest using Benefit Cosmetics "She-Laq" product. It comes with a set of mini brushes to set the rest of your face makeup. It runs $28, but because of the versatility of the product I think it's worth every penny. You can get She-Laq at any department store that has a Benefit counter, a Sephora, or online at
www.benefitcosmetics.com . I always carry it in my kit whether I am doing film, runway or weddings.
These products are all clear liquids. To set your foundation, you spray the sealants on your face (think of hairspray, only for your face

) and you let it set for about 60 secs. For She-Laq, you just dip the little brushes into the container and apply where necessary and also let that set for about 60 secs.
They shouldn't change the way your makeup looks, and if it does then that means you didn't apply it correctly (example: you applied too much and it causes something to glob or streak).
When applied correctly, it will help yoiur makeup to last at least 6 hours. The only time you might have to re-apply anything would be some lipstick because if you eat anything oil-based (salad dressing!) it will cause the sealant to break up, and when you wipe your mouth some lip product will come off.
I wish you the best of luck in finding the right products and for your upcoming wedding!