There are four sources of information, surveys, or programs that produce data on charitable giving. No one of them has a monopoly on accuracy and precision.
The stuff that comes from the income tax returns has some absolute strengths and advantages, but in other respects it has to be taken with great care. Stats Can's presentation was based entirely on income tax returns. Stuff that comes from the Canada survey of giving, volunteering, and participating is a different number. The stuff that comes out of the survey of household spending is a different number. The stuff that comes from.... I could go on.