I second Buffalo, or Niagara Falls NY. Buffalo is a bigger city, so it has more nice restaurants, art gallery, etc. Niagara Falls is a little closer to Toronto. But either way, you should definitely take your sister to see the Falls. It would really be a shame to come all the way from Latvia, and be so close, and miss them. In November some of the tourist attractions will be closed (such as the boat that goes to the foot of the Falls), but there will be no crowds and the views from NF State Park are beautiful.