Hello Wedding Planner,
The closest landing site to Canary Wharf is the Vanguard Site. It's on West Ferry Road, Isle of Dogs. Having said that, there are no facilities on site, ie: Passenger Lounge etc, it's just a disused warehouse with some enough land to accommodate helicopters.
You will need to use a twin engine helicopter. I suggest that you contact one of the London/M25 Based Helicopter Operators and they can provide you with a quote. They will also arrange any necassary permissions that you may require.
It would depend on how far away the hotel is from London, but I would estimate £1,500.00 + VAT
Helicopters & weddings are generally a bit of nightmare though.
Let me know if there is any more information that you need.