This web site may also be of interest,
http://www.equal-marriage.ca/
and provides yet another petition (probably with more
numbers at this stage than the other one I posted, but
maybe for Canadians only) and help in e-mailing your MP
though it may be better to customize your own (including
the subject line, which they don't let you do yet), and to
phone your MP.
But it also provide some info that might be of interest
to non-Canadians.
David