What is the size of the market for executive office centres in Canada?
 Executive office centres are basically shared office space services,
like what's in http://directory.google.com/Top/Business/Business_Services/Office_Services/Office_Space/

I would like a number, e.g. "250,000 virtual offices exist" and a
reference to where the info came from.

Dear eccentrica,

No hard stats, but a couple of interesting tidbits:

www.siliconvalleynorth.com/pdf/ce-toronto.pdf 
Silicon Valley North, March 2003
p.10 "Trading spaces for tech firms"
-no specific statistics, but interesting discussion of the impact on
use of business centres in hi-tech

http://www.coldwellbankerpbr.com/listcp/april_issue4.html
March/April 2001 issue of the Commercial Investment Real Estate
Magazine:
Matthew Stubbs, vice president of sale for Regus business Centres
The office of tomorrow
The following excerpt comes from the March/April 2001 issue of the
Commercial Investment Real Estate Magazine:
Tomorrow’s offices will be located downtown, in mixed use developments
that offer parking, child care, fitness centres, retail, and food and
beverage centres, according to Matthew Stubbs, vice president of sale
for Regus business Centres, in an address at the counsellors of Real
Estate annual meeting.
The strategy behind providing amenities near the workplace is to give
employees less reason to leave work early, he said. In addition, the
office building of the future will be more adaptive to infrastructure
changes. Following the lead of technology companies, offices will have
open floor plans, natural lighting, and movable walls and screens so
space can be reconfigured quickly and easily, he said.

Cheers,
Michael