As you will be here for less than 6 months the cost of buying property, a car etc are all a bit arbitary.
Property Rental in London
http://thisislondon.homesandproperty...earch_rent.asp
Others have given areas to look in. I would look at where you might be placed. Finance centres are around Docklands/Canary Wharf, the E14 postcode, the City EC1-4 postcodes, Other businesses are in the West end WC postcodes. Thats all of the centre. Most people don't live in the centre, but live within the zones 1-4 of the travel card system on the tube.
http://tube.tfl.gov.uk/content/tubemap/default.asp
Also it is possible to look at flat shares, like the sub lease stuff you talk about.
Transport, if you live in or near london you won't need a car. Travel with a travel card and all bus, tube, DLR, Tram and overground lines in the central area are included in the price. If you need to get out of london, the rail network is not bad for getting to cities, or you can rent a car for pennies
http://www.easycar.com/eng/default.asp?R=
Immigration, Visas etc, will be covered by your eer. You dont have an automatic right to work here. You have no recourse to government funds.
Employment, there is a good double tax treaty with CA, so any tax you pay over here will be deducted from your CA tax liabilities.
Think the rest have been covered by other posters. Monthly utils on a small flat should be cheap <£25, TV licence etc
Clothing, unlikly you will shop over here for clothing. It's expensive. Might do to get some nice dress shirts (as you call them) from TM Lewin, give a nice expensive european look when you get back home, thats if you need to wear a suit, not the t-shirt, jeans and long hair software developer look.
International phone calls are dirt cheap. 3p a minute or less to the US (and probably CA), so calling home will not break the bank. If you have a GSM phone then you can bring it over, get a local sim card and off you go (unless it is on the CA GSM1800 network, all green logos - whatever its name is), when it is locked to the network so you will need the handset unlocked.
We use 240V so anything you might be thinking of bringing will need to be happy with a 240v input. PC power supply might need replacing, most other hardware has dual voltage transformers.
There's my bit on this thread.