That's a load of BS. You can come anytime once your permit has been approved. you will of course have to show you meet the requirements to enter including having enough money to support yourself.
You will probably have a hard time finding accommodation while you are still away, mostly depending on where you are coming to.
My suggestion is to find some temporary accommodation (Hotel, Airbnb, etc.) for 1-2 weeks and look for places once you are here. You might be able to find someone willing to hold a room/place for you until you arrive but this will most likely not happen unless you're willing to send money upfront. Needless to say, you will put yourself in a position where you'd be the perfect target for a scam. If you ask me I wouldn't do it.
Get here, and find a place then. Start looking for places shortly before traveling and arrange times to see them as soon as you've landed. The housing/rental market in Canada is pretty tight so be prepared to struggle to find a place to live. Also, expect having to settle for something not great and spending a lot of money.