I recommend you make sure to visit Vancouver and Banff. I wouldn't recommend spending more that 3 days in NY and if you're looking for variety, skip Boston. It's a great city and I'm sure Bostonians will vehemently disagree but it's too similar to NYC. The following cities are probably too far out of your way for you to seriously consider, but I would recommend them for a foreign visitor who wants to get a feel for the range of cultures within the US: Charleston, SC or Savannah, GA, Ashville, NC, Louisville, KY, Santa Fe, NM and Monterey, CA. Washington DC is great place to for Americans to visit, but unless you're into US history or like to see iconic places in person, I would skip it.
If you do go to San Francisco try and plan for some time North of the city. Napa Valley is fairly famous, and beautiful and there are a lot of really nice towns up that way. It's my favorite part of the state.
Seattle is a fun place but you might want to consider Portland OR instead.
I don't know how you like to travel, but I prefer not to be hopping all over the place, however you may never get another chance to come to North America so it might be worth it.
You should have a great time in any and all of the places you've indicated, but you have almost a year to research and plan.