medallion signature guarantee

Google it.

In Canada would seem the obvious answer. Why not try the RBC in Brussels? If they cannot, they should know how.
And google it.

No idea about Belgium (have you tried your bank?), but there are plenty in the U.K.

For example :
https://www.iwcprobateservices.co.uk/overseas-probate-medallion-guarantee/

https://www.fraserandfraser.co.uk/medallion-signature-guarantee/

https://www.lesteraldridge.com/international/medallion-signature-guarantee/

Just a word or warning however, there may be very high fees involved, and if you are administering an estate or inheritance, be careful that you know what you're doing. If this is for shares that you are planning to sell, then your brokerage firm should be able to offer this service as part of the transaction.