The only other option would be to check rates with Sunwing. I am going to assume those rates that you have found are with West Jet... and as a former TA, I'm going to confirm that the lowest you are probably going to find out of Toronto are about $350. Booking flights is like a lottery, you win some, you lose some. It is your gamble! If you want to wait, you might save $50 pp... or, it could go up.
It is June, pretty busy, it'll probably go up. I've been watching January (low season rates) for about 6 months and consider $400 to be a good deal if BUF isn't an option.