With your budget, I would try to spend as little as possible on the receiver, so that you have more money for the speakers. And I would cut it back to a 5.1 system to be able to spend more on each speaker. This also makes it easier to upgrade, if you get money in the future, as you simply buy the extra speakers for the extra channels, if you wish. If instead you buy lesser speakers, then a future upgrade would involve getting rid of some of the gear you are buying now, which will almost certainly mean that you will be losing money. I also do not think that the extra surround speakers are that important, though this will in part depend on how you set things up. In my home, I had a 6.1 channel system, and was so unimpressed that when I upgraded my receiver, I did not bother to change it to 7.1 (which would have involved moving some furniture). I now have gone to a 5.2 system, as my new receiver cannot do only 6 channels (it can do 5 or 7, but not 6). But I digress. If you buy only 5 speakers, you can spend more money on each one, getting better ones, and I think that will matter more than having 2 more channels.
I am not familiar with stores in Canada, so it will be difficult for me to give very exact advice on what to get. (But if you have links to stores in Canada that are worth buying from, please feel free to post them so that I and others can get a better idea of the products available there and the pricing there.)
I would probably go with either an inexpensive Yamaha (I personally have a Yamaha, in large part because I like their feature set and price and, judging from online complaints about various brands, Yamaha seems to be as reliable as you can get) or Pioneer receiver that had all of the features I really needed, keeping in mind that every dollar spent on it means less for the speakers. And speakers matter more for the sound than the receiver. So I would skip any extra features that I only kind of wanted, but did not really need to have, if that savings will be enough to go up to better speakers that will significantly impact the sound.
Another reason to spend as little as possible on the receiver, and as much as you can afford on speakers, is that when, in the future, you decide you need some new feature that is not available now, it is the receiver that you will be replacing, and you will be able to continue using the speakers. So an investment in good speakers gets you better sound now, and the money in them will not be lost when you upgrade your receiver for newer features.
The best way to select speakers is to go out into the world and listen to as many types of speakers (e.g., ribbon, horn, dome, whatever) as you can find, of as many brands as you can find, with music with which you are familiar, of all types of music to which you listen (making a CDR for this is a good idea).
Let us go back to one of your original questions. The speakers that match the Polk TSi500 tower speakers are other Polk TSi speakers. You basically want, particularly for the front speakers, them to have the same tonal qualities. This means that you want them "voice matched", which typically means that they have the same tweeters, and often the same mid-bass drivers. Ideally, it would be identical to the front right and left speakers, but many people do not choose to do that because they want their gear to fit on furniture that they have or want. (In my case, I use identical bookshelf speakers for all channels [other than subwoofers, obviously], so I have perfect voice matching. I will NEVER go back to having merely "voice matched" speakers, but most people are fine with just having "voice matched" speakers.) Now, I am not a fan of such low end Polk speakers (I would want the RTi line or higher), but if you like them best of the speakers you have heard in your price range, and if you have listened to a wide variety of speakers in your price range, you should go ahead and get what you like. (After all, it is you who will be listening to them, not me.)
I see from Polk's website that they make matters more confusing for what they consider to be "voice matched":
TSi | Polk Audio®
However, the subwoofer does not need to match the other speakers in such a way, and so you are free to select any brand you want. If you were in the U.S., I would recommend buying SVS, but I believe that the cost in Canada is higher and may be out of your price range. Polk is not usually what you will find recommended for a subwoofer, though if you got one of their higher models at a very low price and could not afford a better one, it might be okay.
