Flair is a discount airline; do a quick search — they had a few planes seized in March due to missed loan payments, which resulted in dozens of flight cancellations. Haven’t heard anything about financial problems recently, but I’d be careful booking with them. They only have 15 or so planes and if 1 has any kind of problems, that creates a ripple effect across their schedule.
Can you drive to PEI from Niagara? Man that would be a LONG and tiring drive. I personally wouldn’t do it, but it can be done. You’ll be driving across one of the busiest stretches of highways in Canada, if not N. America, so you WILL encounter traffic and construction, how much depends on what time of day you attempt to drive through Toronto. Rush hour is from 8am to 8pm M-F; you might get some respite from 11am to 1:30pm, but I wouldn’t count on it. If you don’t mind a toll highway, you can take the 407 from Oakville (west of Toronto) to way outside the east end of the city. It’s expensive, but you could avoid the worst traffic by taking that route (if you decide to drive). I always take the 407 when heading out of the city no matter what nav says because it doesn’t take much to snarl traffic on the non-toll highway.
I’d personally drive to Pearson and fly. You can fly to Halifax, rent a car and drive to PEI. It’s pretty easy and would provide you with more options. For airlines, West Jet, Porter or Air Canada. Porter just started flying out of Pearson so you might be able to snag a good deal (they frequently have 20% off promos). I like Porter — small planes, but super service and usually they leave on time.