Do you need to incorporate?

Keep in mind when buying a long-term rental, you are deferring the growth till you sell the property.  The only tax is the money earned on the rental, less expenses.  If structured correctly, the income tax will be minimal.

Why would I incorporate?

If you are considering the following, then I would look at incorporating:
Flipping the property; you are considering multiple properties and have a high cash flow; you wish to turn this into a business; you are purchasing something larger than a 4 plex; you have multiple partners.
Keep in mind the extra expense when incorporating.  Two tax returns will need to be done, and the mortgage interest rate will be higher.

For the most part, incorporating will not get you further ahead and if anything will just add a lot of headaches.  For the seasoned investor with multiple properties then it may be worth considering.