Charlotte is the third fastest growing city in the US (http://worldpopulationreview.com/us-cities/charlotte-population/) I know that both Charlotte and Raleigh are both strong for rentals and strong investment plays, but I think Charlotte is a fantastic city to live in.

The information below is either provided by World Population Review, the Kansas City Regional Association of Realtors (KCRAR), or Zillow. 

Maybe this should be number 1, I invest in a small town (population of about 17,000) where the contractors in the area are not used to working with investors.

i'm in sherbrooke. market is pretty hot right now (good multi family deals are sold within days if not hours of listing). most people use centris.ca to listappreciation hasn't happened yet like it has in montreal/toronto/ottawa/vancouver, so its still possible to get good deals approaching the 1% rule (monthly rent = 1% of purchase price) but these properties tend to go quickly. also there's quite a bit of new development happening around the outskirts of sherbrooke, population is growing but maybe not as fast as new dwellings are being constructed. i've seen rental listings where the tenants are offered a free month's rent to sign.i've been renting for the past 5 years in sherbrooke. i payed $420/month (nothing included) for a 3 1/2 from 2014-2017 for a property in murray st.

On top of this, we have a growing medical community for our growing aging population, and we are also starting to attract more entrepreneurs because of the cost of living but still being in CA based location. 

I have been doing a lot of research about the market and noticed that the rent population is about 40% renters.

And if you look at other metrics, the city continues to grow both in population and infrastructure.

These have been the best performing markets and also they have housing shortage working for them (reference Census population/housing unit counts data). 

Is there a rental listing tool in MLS that populates through the aggregators? 

If you're looking for stats on population, employment, income, crime, etc. try city-data.com.