craigm "Air Transat comes up cheapest at about £450, next cheapest direct is BA at £728."
Not sure where you got the BA quote from I have just looked at BA.com and been quoted £639.10. This is for 7th Aug out and return on the 16th Aug. Can't be more specific as you didn't mention any particular dates
DONTTELLTHEPAX
I agree best way is to hire a car, used to go to Toronto about once a year before flying on to see my parents. Whilst downtown, you only need the underground/busses and your feet so you could do a 1 day car hire for niagara. Can I also recommend on Queen St (If I remember correctly) just before it intersects with Yonge St there is a restaurant called The Armadillo - well worth a visit (or at least it was last time I went). Recommend the CN Tower (sunny day and go to the top) also the SkyDome, Hockey Hall of Fame and much more.