Undecided between Toronto or Banff National Park

Looking to visit Canada for the first time. I'm taking roughly 4 days off around the first week of July and can't decide whether to visit Toronto or Banff/Jasper National Park.

I'm flying out of Chicago ORD and it'll be a straight shot to Toronto. On the other hand, if I want to go to the National Parks, I'd have to fly to Calgary with a layover in Toronto. From a timing standpoint, I'd lose more time if I went the Banff/Jasper route.

I love nature more than city life so my heart is leaning towards the national parks. But it'll be a more expensive, time-consuming trip than going to visit and spend a few days in Toronto.

What do you guys think? If I have 4 days, should I visit more of the city life in Toronto or take the nature route and visit the national parks?