The Ontario Ministry of Natural Resources offers you the easiest option of getting your outdoor card and fishing license online. If you have never been fishing in Ontario and you live in the USA, find out more about non-resident Ontario fishing licenses here. You can also purchase them at certain bait & tackle shops or lodges, but there are fewer and fewer businesses that offer that, so it's best to complete it online before you go. You need both an Outdoors Card (good for 3 years) and your fishing license. You need to carry both your Outdoors Card and fishing licence tag whenever you go fishing. You can purchase an 8-day license or an annual license.

You can purchase a conservation or a regular limit license. The difference between the two is the catch and possession limit allowed, and of course, the cost. Ontario has many different fisheries management zones, so know which one you'll be fishing in. Your lodge or outfitter can tell you. Some lodges sell fishing licenses, and some do not, so make sure you ask. If they don't sell them, many bait and tackle shops across the region do. Follow catch and possession limits and have a great time. 

Canadian residents can get more info on obtaining a license here.