Seahawk games are a blast so the game day experience should be a lot of fun for you. I've been there enough to have developed a preference for the north end of downtown (Hyatt / Westin / Crowne Plaza area) for accommodations. You can usually find decent deals on expedia, etc. The south end of downtown (starting a block or two north of Yesler and going south) is scuzzier with lots of street people, meth heads, et al. They generally keep to themselves but there is the odd one or two aggressive ones. It's a little bit worse after sun down.
My favorite place is the Arctic Club due to its sort of mid point location in downtown but it's got stupid expensive in recent years (keeping pace with Seahawks tickets, I guess). Second choices would be the Sheraton Seattle and then the Alexis (although it's often pricey too). I will be checking out airbnb and VRBO options this year. Something like this:
https://www.airbnb.ca/rooms/5060388?...s=4&s=g8-HQ9eL. is a good deal for four people.
If you are driving you'll find parking expensive as previous posters have said. Once you are situated, anything you would need for food and attractions is mostly within walking distance. It's actually pretty enjoyable to walk from the north end of downtown into the stadium area early in the day, find a drinking hole then mosey over to the game. Seattle is much like Vancouver with lots of older architecture and things that you won't see in Calgary. We've done lots of different stops but tend to migrate to Safeco ($1 to get in) to watch Red Zone on the big screens prior to the game. Beer, including a great selection of local craft beers, is way cheaper at Safeco than at Clink (where the real wallet thinning begins). There's a convention center between Safeco and Clink where there's all manner of football-related stuff. Usually cheerleaders signing things and doing photos, a live band, booths with contests and all that kind of stuff. And more beer, of course. You may wish to bring ear plugs.