The drinking age in this province is 19. If you were born after 1999 you will not find anything of interest here for now.
Whether you are shopping for yourself or for a large party, Ottawa offers a wide variety of beer and liqour stores. Mostly, you're stuck buying from your neighbourhood Ontario Liquor Store or the Beer Store. The Beer Stores are operated on behalf of the large breweries (so you may not always find the micro-brewed brands) Liquor stores also sell beer, but usually international beers and very popular Canadian brands.
Around the province, you can buy beer or wine, in stores run by the makers themselves, typically a micro-brewery (like the Upper Canada Brewing Co.) or one of the many fine Ontario wineries. So take the time to find one that has the items you like or is willing to special order them for you.