Expect to pay between $600-$800 when flying from YYZ and between $400-$600 when flying from BUF. However, it's not uncommon to see fares over $1000 from YYZ. Often a package is the better way to go.
There are a ton of great hotels on the strip in Vegas it all depends on where you want to be and how much you are willing to spend. I've been to Vegas about 20 times. We usually stay at Ceasar's but have stayed many other places as well. If you are looking for budget accomodation a great pick is Excaliber...it's been fully reno'd in the last few years and is south strip. If you are willing to pay more then center srtip is Planet Hollywood, Bellagio, Paris and Ceasar's. A bit further to the north is Mirage, Venetian and the Wynn. I avoid downtown as it's too far from everything else and it's a little seedy.