I agree about the issue of the phone being charged. Lithium ion batteries in modern phones self-discharge at a fairly rapid rate. You'll want to charge the phone a couple of times a month at a minimum. Luckily, lithium ion batteries love to be topped up regularly (they don't need to be drained first, despite what many people think). I have a Virgin Mobile phone that sees very infrequent use (less than an hour a year) and the battery is still going strong after 3 years because of regular top-ups.
As for the carrier, your first concern should be coverage. If your phone is for emergencies and your phone won't work when you have one, it's not doing you any good. Essentially there are two networks in Canada (slightly oversimplified but accurate enough for the purpose). There is Rogers, which uses a technology called GSM, and there is Bell, Telus, Aliant, SaskTel, MTS and a few tiny regional carriers, which use a technology called CDMA. (Bell and Telus overlap each other somewhat, but still permit you to use the other's network, which is why I lump them together.)
There are also MVNOs (mobile virtual network operators). Petro-Canada, 7-Eleven and Fido are MVNOs running on Rogers. President's Choice and Virgin are MVNOs running on the CDMA networks.
If the Rogers network will do, Petro-Canada and 7-Eleven are hard to beat. If not, you will want to check out Virgin and President's Choice. I don't know the fine print on the PC offer, but Virgin gives you a year for a $100 top-up.
Another, slightly peculiar option if you think the Rogers network will do is to use T-Mobile USA. If you put $100 onto the phone in the first year, you get a full year of validity. After that, $10 top-ups extend your expiry by a year. In the long run, this will be your cheapest option for very infrequent usage. The catches are that your airtime in Canada will cost 59 cents a minute, and you will have an American phone number for incoming calls. (I gather the phone will never be on unless you are making an outgoing call, so the incoming number is largely irrelevant.) On the plus side, you will have a perfect phone to use when you travel to the US. Instead of paying a dollar or two a minute with a Canadian provider, your rate will be in the 10 to 20-cent a minute range (depending on what top-ups you've used; cheaper top-up cards have a higher rate). You can get preactivated SIM cards for T-Mobile off eBay for about $10-20, and will need to buy an unlocked GSM phone that supports the 850 and 1900 MHz bands (pretty easy to find and not expensive). Petro-Canada's phones at one time were not locked, but I'm not sure if that's the case anymore. It might be safer to get one off eBay. (If you think you will travel overseas, get a quad-band like a Motorola RAZR V3 and it will work just about anywhere that has cellular coverage.)