But I was wondering is it possible to find a decent paying job like working in a restaurant, a warehouse worker, customer service in a mall or something like that?
There's no such thing as a decent paying job in a restaurant, customer service or in warehouses. Furthermore, how would you expect to work in Poland without knowing Polish and with a lot of Ukrainians (that can more or less understand and be understood in Polish) willing to take such jobs?
Furthermore, you're Canadian. That means you need a work permit, which no-one is going to apply for on your behalf when they can just employ a Ukrainian student that doesn't need a work permit.
Basically I want to find a job Mon/Fri so I can travel a little bit throughout Europe on weekends (like a 1 day trip to germany and stuff like that) as it is very cheap to do so.
It's cheap if you earn a good salary. You won't get a good salary working in the lowest jobs.