If you do not have a contract then there will be no fee to cancel you will just need to pay for the days the phone was active before it was canceled. If you are planning on coming back and would like to keep your number and plan you might want to consider doing a temporary suspension.
A temporary suspension is only for lines that is currently not on contract and it can be added for 2-12 months and the cost is $7/month.
If you are on contract then you will have to pay the remaining device balance plus the days the line was active before you cancel.
If you want to do the temporary suspension or cancel the account only a Fido representative can do it, you would need to get in touch with them.
To contact customer service even from outside of the country see here.