"Evidence of their authorized stay may include: an entry stamp in their passport, a temporary resident
record, a work permit, or a study permit. Evidence of being a temporary foreign worker or
international student may include: letters from employers or schools, records of pay, attendance,
report cards, transcripts, etc. Evidence of being in Canada may include a residential address and
correspondence sent to that address. These examples of evidence are neither exhaustive nor
exclusive.
Persons in Canada who have been studying or working here throughout a one-year period, during
which they were also subject to an unenforced removal order, are not legally residing in Canada.
Their applications are not eligible for placement into processing under Ministerial Instructions."
p. 14, http://www.cic.gc.ca/EnGLIsh/resources/manuals/op/op06-eng.pdf
If your mailing address is in Canada, you have a work permit , and a letter of employment - all of which you have to submit anyway - you probably don't need any further documentation.