Given that you would be competing for one of the few non-resident spaces in a very well-regarded school, I think you would need at least a 90% to make the cut. The average for the last several admitted classes was 86%-88%, and there are only about 12% of the seats for non-residents so you'll probably need to be above average.
Have a look through the admissions page for international or Ontario residents, whichever fits your situation (http://www.ovc.uoguelph.ca/recruitment/en/index.asp). There are approx 15 spots available (100 Ontario undergrads, up to 5 Ontario grad students, ~15 international=120). Intake is ongoing, there were interviews in November and March this year. International admission stats are not published but I expect they are similar to the Ontario undergraduates (last 2 semester & prereq averages in the high 80s for the last 4 years).