Sprint offers roaming for Canada, though I'm not sure if they have service for "pay as you go"
They offer a regular rate of 59c a minute, but you can pay $2.99 to get a discounted rate of 20c a minute.
Traveling to Canada? For only $2.99 per month all calls placed from Canada are only $0.20 per minute! Whether you place a local call in Canada, place a call back to the US, or receive a call with the Canada Roaming Option you pay only $0.20/minute (without the plan calls are $0.59/minute).
In the case of Tracfone, there are actually two different Tracfone services, though most people don't realize it. Tracfone CDMA and Tracfone GSM. In Canada Tracfone CDMA is on the Bell network and Tracfone GSM is on the Roger's network. Depending on which network and plan you can be charged either the regular rate or double rate for calls (it should indicate on the phone).
Tracfone does offer an interesting service called International Neighbours that gives you a local Canadian number to reach your cell phone. Basically someone in Canada can dial a local number and have it ring on your cell phone. So if a family member has a tracfone they can get this service and you can just use a pay phone or make a local call to talk to them.
TRACFONE International Neighbors is a service that enables callers in Mexico and Canada to set up a local number to ring on a TRACFONE in the US. (Please call 1-800-867-7183 for details).