The rear wiper doesn't work as well, and i'm wondering if the two problems would be related to eachother? Is changing a circuit breaker like changing a fuse? And if I replace the circuit breaker, and it still doesn't work, what are my next steps?

If a new breaker doesnt fix it, pull the carpet up on the drivers side and check the wiring for any chaffing, etc.. Check the connections for any corrosion, too. Trace as much wiring as possible.

Where can I get a circuit breaker from? Just any Canadian tire? Or do I need a specific part # for it?

Any automotive shop should sell them. Walmart and the like usually have a small selection. As long as it fits and is of the proper amperage i wouldnt worry about the part #.