I went with Air Canada Rouge to/from Manchester. Transport from airport to downtown Toronto is cheap and regular (approx. £7 by train, 20mins and £2.50 bus/subway, 1hr). The ground is a 30mins or so walk from the centre west along King Street - there is also a tram that stops right outside the ground. For a pre (and/or post) match beer with the friendly locals, walk down Atlantic Ave (just east of the ground) from King St West , turn left on to Liberty St and walk till you get to the 3 Brewers pub.
Single journeys on the bus/subway/tram system cost CAD3.25 (approx. £2.50) and allow multiple hop ons and offs for (I think) 2hrs from 1st scanning in. The city (and transport system) felt safe even late at night.