Right where to start! (this is a great excuse for me not to revise so thank you)
Yes I did go through BUNAC, some people who had been before advised me not too but I thought it was worth paying that bit more to have someone sort your visa out for you (the hard bit apparently) and for going on the group flight so that you can meet people on the plane and start forming a little plan (I originally had all these wild plans about flying there and doing all these things by myself... I ended up staying with a group of 7 people and going to Whistler and staying there all summer)
I took about £1200 with me, they say they check but they never did so i presume it will be the same for you again. My advice is just to take as much as you possibly can... things always come up out there that you should have sorted before you got before you left the UK or thing you should have bought etc. Besides the extra money is always handy for buying the first round for your new found friends!
Before you even think about work and housing, decide where you want to go in Canada. There are only two main options, big cities (Vancouver, Montreal, Toronto etc) or resort towns (Whistler, Banff, Jasper etc) I personally stayed about a week in Vancouver (where I flew too) and then headed up to Whistler. I think its down to personal choice, as much as I loved Vancouver its too big just to walk around so would have had to fork out for the bus etc... I know it sounds silly but little things like this soon add up. I got the greyhound (bus) up to whistler (get a Hostelling International card, these are avaliable from the hostel opposite the one BUNAC put you in for the first few days, presuming you stay in the same sun.. this card gets you 30% off greyhound fares and is definately worth it!)
So me and about 8 people went to Whistler, found a house on craigs list that we could stay in for 10 days to get ourselves sorted and everything. We spend about a week job hunting, we all found jobs in either retail or food (I worked in cows ice cream, the best job I have ever had). The earlier you get out there in summer the better, obviously companies like to hire before the season gets into full swing. You need to be persistant with job hunting, hand in your resume go back in after a few days, talk to the manager and chase it up.
Housing wise again it depends where you want to go, WE all found a lush 11 bedroom house with a sauna and jacuzzi and think we were paying 400 dollars every two weeks which isnt all that bad.
First things first, decide where you want to go.. if its Whistler let me know and I have even more advice, same for Vancouver (from what I remember BUNAC only fly to Vancouver and Toronto, so this will play a big part in your decision). Once you have decided start looking into houses in that area and the price etc, craigs list is a god send just watch out for scams etc.
You said your main concern was finding some where to live, it really isn't that hard dont worry, if it comes down to it just have a few more nights in a hostel. Everyone I know who I flew out with found a house within 2 weeks so you will be fine, just make sure you have enough money to pay a deposit. ooo yeah before I forget, make sure you get the forms from SWAP (these are the people bunac pass you on to in Canada, they get you started up and everything) that allow you to not be charged tax, I am trying to claim mine back now and its a right pain!