It's French land which they're allowing Canada to use for a specific purpose for all time.
The original treaty is Agreement Between Canada and France for the Cession to Canada of the Free Use of a Parcel of Land on Vimy Ridge for the Erection of a Monument to the Memory of the Canadian Soldiers Who Died on the Field of Honour in France in the Course of the War 1914-1918.
Article I: The French Government grants, freely and for all time, to the Government of Canada the free [use] of a parcel of 100 hectares located on Vimy Ridge in the Department of Pas-de-Calais, the boundaries of which are indicated on the plan annexed to this Agreement.
Article II: The Canadian Government pledge themselves to lay out this land into a park and to erect thereon a monument to the memory of the Canadian soldiers who died on the field of honour in France during the war 1914-1918.
They moreover pledge themselves to provide for the maintenance of the park and monument, in default of which the French Government would resume the free use of the park, except however the land on which the memorial is to be erected.
Article III: The land granted to the Government of Canada by this Agreement will be exempt of all taxes and imposts. The French Government will take the responsibility of all difficulties with the borderers, except those arising from damages caused by the personnel or material belong to the Government of Canada and kept in France for the maintenance and protection of the park and monument.
Suppose I want to open a gift store in the area. Does France or Canada have the authority to grant the license?
You would probably contact Veterans Affairs Canada who runs the site.
If VAC did allow your store, France could object that your gift shop does not fall within the terms of the grant.
Congratulations, my license is granted! Does my store pay taxes to France or Canada?
Article III says "the land" is exempt from taxes which probably means property taxes and the like. I doubt that applies to transactions done on the land. If you do pay tax, it would be to France. Fees for being allowed to run the store would go to Veterans Affairs Canada.
Oh no, someone robs my store! Will they be prosecuted under French or Canadian laws?
The French hate my poutine and want to close the store. Can they legally take back the land without Canadian consent? Invasion doesn't count.
If the French agree the grant allows the Canadians to sell poutine, the French probably cannot shut you down just because they don't like the food, but they could
take you to the Hague because bad poutine is a crime against humanity complain to Veterans Affairs Canada.