What is the size of the investment management sector of the North
American financial services , in terms of assets under management?

Great question!

The Investment Company Institute tracks a large amount of information
about mutual funds and pension funds.

Their "2002 Mutual Fund Factbook" says that there are $7 trillion in
assets under management by 8,307 companies with 248 million
shareholder accounts:
http://www.ici.org/pdf/02fb_datasec1.pdf

The ICI Mutual Fund Factbook covers U.S. only.  Inasmuch as the
Canadian economy is 10% the size of the U.S. economy, adding 10% to
U.S. market size is often a safe assumption.

Best regards,

Omnivorous-GA