As per this document they must provide something others then liquor:
http://aglc.ca/pdf/liquor/liquor_laws_&_you.pdf
Page 18:
"1. Can I charge for water?
Yes. However, all prices must be posted.
2. Can I insist all of my customers buy something to stay in my premises?
Yes. However, you cannot demand that they buy liquor; they could be asked to purchase a
non-alcohol drink for example. You could also consider implementing a cover charge."