Hours are dependent on projected sales, how many cashiers are available, and when peak hours for sales will occur. Generally you can expect your highest hours earnings to happen on the weekend, assuming Canadian shoppers follow similar shopping habits as Americans.
It also will depend on your availability (what hrs you can work).
Sometimes they will call you on a day off & ask if you can work a shift because someone called out.
Sometimes they will call you on a day you're scheduled to see if you can come in earlier/stay later.
If you're flexible, it's a good way to pick up hrs.