You have to convert the GPA by assigning each class its correspnding value.
A+ (12)= 4.33
A (11) = 4.0
A- = 3.67
For law school the 4.33 scale is always used in the US. As for the marks from Canadian schools being given a boost, I have heard some people say as much but no one seems to know for sure. I think us Canadians are just a bit out of luck, when you look at US schools with median GPAs around 3.4 compared to Canadian schools where classes seem to be curved at a C+ or B-.