For those of us not in WNY its good to refer to the casinos by name and location. I learned the differenences on my recent visit.
Seneca Niagara ( American Side )
Casino Niagara ( original on Canadian side across from American Falls)
Fallsview Casino ( new on canadian side closest to horseshoe falls)
Fallsview is sort of like a vegas style with the hotel, shops, restauraunt and casino. Seneca will be similar but Hotel isnt finished as of May.
We actually liked the Seneca best, seemed like one armed bandits were looser than in Fallsview.
If you are planning on going to canadian side casinos from Buffalo I still think best bet is going over Peace Bridge, customs seems always easier than on rainbow bridge.