Also you can buy prepaid Canada Post boxes for a little less then $20 if
that helps.They are called flat rate boxes and you can buy them at any
Canada Post. You can ship anywhere in Canada for that price as long as
it fits in the box.
You can message Ebay on Facebook and might be able to get the feedback
removed. The feedback is clearly an error. I had something similar
happen and Ebay removed the negative feedback for me.
From that picture it might fit through the Canada Post slot. Sometimes
items might be slightly over or the bubble wrap inside might make it
hard to push through. Or an item I am sending barely fits through so I
just stamp it and put in a red mailbox....