If you are a Canadian resident you can travel with a Eurail pass not Interrail.  

If you fullfill the conditions for entering the Schengen area you can travel within the Schengen area for 90 days with a Canadian passport. You need to check the conditions yourself.

Bulgaria is not a part of Schengen and you need to check yourself if you can enter Bulgaria without a visa.

Canucks with a true blue maple leaf passpt are among the best loved people in this whole world in getting visa-free access in many countries-incl all these. BUT as winter comes there may again be some newtocome extra anti-covid measures-nobody will know that now.

As this is a train-only forum: be aware that train is not the very best choice for this routing and in fact in some cross-borders even impossible-best site for overview is seat61.com. This also means that a pass is probably throw precious CA$ out of the window-just buy locally-as also fares in PL-SK-HU are fairly cheap-a lot lower as VIA charges for same distance. And use bus or whatever if that is the better chocie for that sctor.

For general info+more tips: do a generic forum like tripadvisor.com