Should be fine.
Canada VISA http://www.cic.gc.ca/english/applications/guides/5256E2.html
"A single entry visa allows you to enter Canada only once. This visa may also
be used for repeated entries into Canada from the USA or St. Pierre and
Miquelon provided you do not enter another country. Such entries must occur
within the time validated for your stay in Canada.(e.g. You may be given six
months from the date you enter Canada at the Port of Entry) "
I know my friend did this too.
