From the information we could gather it would appear that your uncle could legally drive in Canada by having his valid foreign (Brazilian) license and the international driving permit. Canada and Brazil are both members of the 1949 International Convention on Road Traffic meaning that they both allow foreigners to drive in their countries when they follow certain conditions.

Canada International, a Canadian government site for non-Canadians (canadainternational.gc.ca) states that drivers from outside North America are advised to apply for an International Driving Permit from an automobile association in their country of origin. The IDP is then used as proof that the holder possesses a valid driver's license issued by a competent authority in their home country.

Also according to this site, in Canada, the International Driving Permit is required in order to rent a car. To find out if Canada has any restrictions on foreign licensed drivers by contacting Canada International, Transport Canada (www.tc.gc.ca) or the ministry of transportation for your area of Canada which you uncle plans to drive in.