Like in Milwaukee and Seattle, an outdoor stadium is unfeasible in Toronto due to cold weather in April and October, and being in higher latitudes. Remember why Skydome/Rogers Centre was built in the first place:
Per Wikipedia:
"The main impetus for building an enclosed sports venue came following the Grey Cup game in November 1982, held at the outdoor Exhibition Stadium. The game was played in a driving rainstorm that left most of the crowd drenched, leading the media to call it "the Rain Bowl". As many of the seats were completely exposed to the elements, thousands watched the game from the concession section. To make a bad experience even worse, the washrooms overflowed. In attendance that day was Bill Davis, the Premier of Ontario, and the poor conditions were seen by the largest TV audience ever in Canada (over 7,862,000 viewers) to that point. The following day, at a rally at Toronto City Hall, tens of thousands of people who attended the game began to chant, "We want a dome! We want a dome!""
At this point, a full blown renovation of the Rogers Centre (which is in the plans) is more likely than a new stadium. If you want a team that really needs a new stadium, try Tampa!