I agree with you on the varying "leagues" (lieux ou lieues) - the 2.4 mile lieue de poste was ~= to the 2.4 mile lieue de Paris; but Paris was Paris, and Quebec was (well) Quebec.
So, here's a Quebec example from 1647 to 1765, originally the 1647 Seigneurie de Repentigny:
Though later subdivided, the exterior boundaries remained the same - as in 1765 (my ggm was from Mascouche (St.-Henri); my wife's ggf was from l'Assomption):En 1647 premiere concession de la seigneurie a Pierre Le Gardeur ecuyer sieur de Repentigny. Cette seigneurie avait quatre lieux de front par six de profond et elle etait bornee au sud par les rivires Saint-Laurent et La Chesnaye (Des Mille-iles), a l'est par la seigneurie de Saint-Sulpice, au nord par les Laurentides (futurs cantons de Kilkenny et de Rawdon), puis l'ouest par ce qui sera plus tard la seigneurie de Terrebonne (1673).
Charlemagne (Celine Dion's hometown) is located on the west bank of the mouth of R. l'Assomption; Terrebonne is just west of the 1647 (and later) west boundary. The distance between Terrebonne and Charlemagne is just over 2 leagues (deux lieux; 1/2 of the original front).
The distance in miles between Terrebonne and Charlemagne is 7.42 miles (crow flies) and 9.32 miles (motorway; which seems to be what the 1647 description contemplated - following the river banks). Divide by 2 and one is closest to your Spanish league (straight line), or to Bearor's high of 4.6 miles (following the river-motorway, Chemin St.-Charles). Unless one finds compelling reasons to do so, picking the low of the 2.4 to 4.6 mile range seems a bit "forcing".
I'll be back with some French-Canadian links and some pdf pages to attach - so everyone can follow the key original sources (Bearor's first step, which may have some stumbles in it).
Regards
Mike
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