I really don't know anything about other schools. I was sent information about funding with my acceptance letter. So, if you got in without any mention of funding, then the schools might be operating differently. I would expect the amounts offered to differ though: for one thing, my school promises a minimum of 22k. It's also safe to assume that each funding offer is unique to each student (though definitely would fall into a range, which itself is unique to each department given its own size/financial standing).
I wouldn't worry about it too much at the moment. If they say they're offering a minimum of 18k, then you've got something to work with (if you must plan now, planning as though you'll receive 18k might be a good plan). If it helps, I think it's quite fair/acceptable to write them an email and ask when you'll be hearing back about funding.
I am also an international student, so we might be in the same boat. I think when you apply, you're automatically considered for the International Graduate Tuition Award, which amounts to about 3k that goes towards paying your tuition fees. That's something to ask about as well.
Hope this helps!
P.S. I'm not sure what links would be useful but here's an ugly looking one with the details about the International Graduate Tuition Award: https://iac01.ucalgary.ca/FGSA/Public/SpecificAward.aspx?AwardID=5925