Is it possible to become a commercial pilot if one suffered from depression in the past?
I really can't speak for the Canadian standards for Airmen Medical Certification, though I did find this on Transport Canada's website.

https://www.tc.gc.ca/eng/civilaviation/regserv/cars/part4-standards-t42402-1412.htm

Transport Canada also lists the following concerning anti-depressant medications (SSRIs).

https://www.tc.gc.ca/eng/civilaviation/opssvs/cam-ssri-347.htm

This sounds very similar to the FAA's position in that people who are diagnosed with depression requiring medication are prohibited from obtaining a medical certificate.

OK, don't throw yourself off a bridge just yet; there's some good news.

The good news is that this is applicable if you are currently on mood altering medications perscribed by a physician.  If you have a prior history of depression but are not currently on any medication, there is a good chance that Transport Canada could issue you a Special Issue medical certificate, if you are willing to go through all the extra paperwork and documentation with your physician.  You are going to have to document, probably with the written concurrence of your physician, that you are no longer depressed, your case history was acute, not chronic with recurring episodes, and that you no longer require medication to maintain a normal mood.  Transport Canada will probably issue you a Special Issuance Airman Medical Certificate, valid for about a year, which will allow you to obtain your license.  As long as you are not diagnosed with further episodes of depression during this period and your doctor can confirm this, TC will probably issue you a regular airman medical certificate thereafter.

What I would suggest is that you make an appointment with a physician near where you live who is a Designated Medical Examiner for Transport Canada and talk with them about what TC's disopositon is on disqualifying conditions for medical certification.  NOTE WELL: Do not - NOT - make the appointment so as to indicate that you want an official airman medical certificate examination; we do not want any kind of official diagnosis entered onto your permanent record with Transport Canada just yet; this will only complicate things and we need to know exactly what TC's position is on these issues BEFORE we proceed down that road.  Select a DME who is also a pilot and will tend to be more sympathetic to your plight.

I hope that helps and good luck to you on your future aviation endeavors.  There is hope for you.