A single entry visa may be used as a multiple entry visa within its valid duration. When you return to the United States, you may request re-entry to Canada at a port-of-entry (Canadian site) as often as you wish during the time you have been authorized to stay on your first visit.
Example: You have been issued a single entry visa valid to August 05, 1997. You must enter Canada BEFORE August 05, 1997. If the officer at the port-of-entry grants you a six months stay (to February 05, 1998), you may request, at the port-of-entry, to return to the USA and re-enter Canada as often as you wish until February 05, 1998.
Example: You have been issued a single entry visa valid to August 05, 1997. You must enter Canada BEFORE August 05, 1997. If the officer at the port-of-entry grants you a six months stay (to February 05, 1998), you may request, at the port-of-entry, to return to the USA and re-enter Canada as often as you wish until February 05, 1998.