The canadian side of Niagara Falls is quite beautiful. It's often booked up on weekends, but Yosemite is a real pleasure and you can get some great deals during the week. You should look to rent a vacation home, so you'll have things like running hot+cold water and even satellite TV. Fly in to Oakland or SFO (oakland is closer), rent a car and take the ~4-hour drive up. The Cathedral Rocks are a true natural wonder as is Yosemite falls. If you have never been to the mountains, the sense of scale in Yosemite is really something else. Enjoy your time together and have a happy trip.