The upper class grows wealth and the lower class grows population.

I will tell you what works for me. I usually leave the taxes set as they are but I exempt the regions from taxes that I want to grow quickly.

It has a more significant effect than lowering taxes on growth and you can usually do without the money from that region for a few turns. You not only grow the population in that way but also the wealth.

Rupert’s Land is the place to start. You will have a town there in short order, and I recommend you build a school to advance your techs. Also improve the Barracks to get troops there quickly. You will be fighting Indians and French in no time.