How do I legally get into canada after I got deported from the us to italy on a drug felony

You wouldn't be able to normally, they would be able to see this deportation order and the drug felony.

You can contact the Canadian Embassy in Italy (if that's where you are now) and ask them if you can apply for what is called "deemed rehabilitation" it's basically asking the Canadian Government to allow you entry even though you have a criminal record.