Do not go with any of the three large brands (unless you are a big company with good price leverage). They will lock you into an expensive 2 or 3 year contract and prices are set to fall! You will still be paying huge amounts when the price points have dropped! So don't get locked in, even if the latest iPhone is very shiny on the shelf. If you are moving in, bring unlocked phones that work on the frequencies you need. (If you are going back and forth, some better Nokia phones are best: They are the only brand that has 5-band HSPA support.)
It is hard to buy unlocked, modern phones in Canada! There is hardly any phone market except for the operator's locked offers.
What is a good plan for you depends on where you are going to live and how you are going to use your phone. The new and cheaper networks (like WIND and Mobilicity) are only in the big cities. In these provinces, the bigger brands have lower prices then in other provinces. In some other areas, new networks are being built (for instance by Eastlink in Atlantic Canada) - so prices will drop there later on.
Personally, I have found Koodo Mobile to have the best offer - it is still extremely expensive compared to most European markets, Canada has the highest mobile telephony prices in the world. However, Koodo does not lock you in, you can cancel at any time. In most price plans, they don't charge extra for text messaging (the big brands will charge you even for receiving texts!) and Koodo's text messaging includes text to other countries. (Receiving texts from abroad might not work, depending on the operator texts are coming from. Koodo blocks incoming text messages unless there is a special contract.) With the LD & International Saver Add On for 2$/month you can make phone calls abroad for as little as 5 Cents/Minute. They have price plans with unlimited calling or unlimited incoming calls, and with a Nationwide Add On you don't have to think about where you are or where you are calling to in Canada. This is important to me because often you can not know from a phone number where that is (e.g. 902 is the area code for all of Nova Scotia and PEI - but if you are in Halifax most of the area would be Long Distance!).
All Koodo customers that are on the same contract can make local phone calls with each other for free. This is called Family Calling.
10% of your bill are returned to you in form of a "Tab" credit. You can collect up to 150$ that way and use them to buy a new phone. I think Verigin Mobile has something similar.
This winter, I've spent a lot of time investigating all the offers, and Koodo was the best for my needs since there is no Wind or Mobilicity in my area. Customer service could be better, they don't know a lot about their own business.
If you decide to go with Koodo and you know anyone who is already a Koodo customer, get a referral code for them. It will give both of you 25$ on the "Tab".