The institution you’re thinking of is the Académie française. The linked Wikipedia page has a wealth of information including links to the counterpart in Quebec.

The Organisation you mean as “the worldwide canonical guardian of the French language” is the Organisation internationale de la francophonie. Their website is http://www.francophonie.org/

They have 54 members: 52 French-speaking countries (including Canada) and the Canadian provinces of Québec and New Brunswick.

They also have 3 associated countries (which are not full members) and 23 countries that participate just as observers. http://www.francophonie.org/-80-Etats-et-gouvernements-.html

They are based in Paris. Their address is:

19-21 avenue Bosquet
75007 Paris (France)

Téléphone (33) 1 44 37 33 00

Télécopie (33) 1 45 79 14 98