The parts in your build are imbalanced. The hard drive is very overpriced, while the basic motherboard is older and not as well featured. Actually, the motherboard may not work with the i7 4790 out of the box because H81 motherboards need a BIOS update to work with Haswell Refresh line of processors that includes the 4790. Also, the 4790 cannot overclock, only Intel K model processors like the i5 4690K and i7 4790K can be overclocked. If you want the ability to overclock, it will come at a cost premium as I recommend a Z97 motherboard for it.
You also chose a laptop sized (2.5") hybrid hard drive. That WD hard drive is mainly meant for laptops as a way to save space as it combines a 1TB 5400RPM hard drive with a 120GB SSD in one package. It's also extremely expensive for the amount of storage it offers.
1. All motherboard should have options for overclocking, but it varies from model to model. I expect enthusiast level motherboards (Z87/Z97) to have more and better tinkering options than budget minded H81/B85 motherboards. I'm not exactly sure what you read about Haswell being hot, but the 212 Evo should be more than good enough to handle the 4790's TDP.
For undervolting it's hard to say, actually. Best options are to search around user comments/reviews and ask if anyone's successfully undervolted with a specific motherboard model, or stick to Z97 and maybe H97 enthusiast motherboards for that.
2. It depends, but usually cases come with fans. I know the Cooler Master N200 you selected was reviewed by Tweaktown and they liked it for good design and strong construction. The design allows for good airflow, but they noted that temperatures were average and it does need extra fans to do better.
3. I'll look for a case. I assume you want it compact with good airflow more than anything else? By "headphone and USB ports at the bottom of the case", do you mean you will have the case upright on a table and want the ports low and in front for easy access? There are few to no cases like that, usually the buttons and ports are all located either front facing at the top or upward facing on top of the case. The Cooler Master N200 won't lay perfectly flat as the side panels bulge outward.
Almost all cases are designed with upper frontal USB and headphone ports... what about standing the case upside down? You can buy
stick-on rubber feet for less than $3 and that will help balance the case.
4. As for Canadian prices.. it varies, really. About 4 months ago I picked up a Toshiba 3TB hard drive for $99 CAD on sale, now a decent 2TB costs around $95 CAD. I don't know of any upcoming sales.
I'm working on a parts list for you, but some answers to whether or not you want overclocking and whether you want a compact PC will help to narrow down choices.
