I would not go all that way for 7 days see if you can squeeze in an extra few days.
Do not forget you pretty much lose a day flying over.
I would look at Oceania or Azamara they are upscale but not high end like Regent and have open dining (freestyle)
Alexandr Pushkin, Carnival-Holiday, HAL-(old)Westerdam, Orient lines-Marco Polo, Royal Olympic-Olympic, NCL-Dream, Dawn-Princess, ACCL-Grande Caribe, Oceania-Insignia (3), Regatta(4) Marina (1) St Lawrence Cruise Lines-Canadian Empress
Scenic River cruise June 11,2012