I live in Canada and I would like to know if I can work as a real estate agent selling houses?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Initially it is lawful to buy and sell from non-Muslims including being an estate agent.  The evidence for this is the Hadith reported by Al Bukhari from Ayisha (Radiya Allahu Anha) who said: "The Prophet (Sallallahu Alaihi wa Sallam) bought some food - with delayed payment - from a Jew and he mortgaged his armor until the price of the food was paid back".  But if selling to non-Muslims can result in something forbidden, then it becomes forbidden as well, like selling them weapons to fight Muslims.

Also, it is unlawful to sell houses to people when the person is certain that they will use those houses in forbidden things like selling wine, or brewing it, or selling pork, or the like.  Or if the person knows that they will turn those houses into pubs or gambling places or prostitution houses.

To conclude, it is lawful for the Muslim to sell houses to non-Muslims provided this will not result in harmful effects.

Allah knows best.